George Washington University's Program on Extremism said in the study that the number of other Americans who passively "consume" Islamic State propaganda runs to "several thousand," though they are not necessarily active supporters of the group.
Twitter is the "platform of choice" most widely used by the active core of American supporters of Islamic State, it said.
People who were interested in ISIS from other countries:
People accused of trying to join ISIS/recruited by ISIS
Islamic State's online supporters include 300 Americans: report
FILE - In this Feb. 24, 2016, courtroom file sketch, Tairod Nathan Webster Pugh, right, sits at the defense table with his attorney Zachary S. Taylor, during jury selection in a federal court in the Brooklyn borough of New York. Pugh, a U.S. Air Force veteran and former airplane mechanic charged with trying to join the Islamic State group, was convicted by the jury Wednesday, March 9, 2016. It was the first verdict to result from more than 70 cases the government has brought against U.S. citizens accused of trying to support the militant group. (AP Photo/Elizabeth Williams, File)
In this Oct. 5, 2012 photo, Jaelyn Young, an honor student at Warren Central High School, poses for a photo in Vicksburg, Miss. Young and another Mississippi resident were arrested on Saturday, Aug. 8, 2015, on charges that they were trying to travel abroad to join the Islamic State militant group. (Melanie Thortis/The Vicksburg Evening Post via the AP)
In this courtroom sketch, defendants Noelle Velentzas, center left and Asia Siddiqui, center right, appear in federal court with their attorneys, Thursday, April 2, 2015, in New York. The two women were arrested Thursday on charges they plotted to wage violent jihad by building a homemade bomb and using it for a Boston Marathon-type terror attack. (AP Photo/Jane Rosenberg)
In this undated image taken from video released by Turkish broadcaster A Haber on Friday, March 13, 2015, a girl, left, believed to be one of three British girls on their way to join the Islamic State Group in Syria, is seen in Turkey. A Turkish news channel released a video that it says was recorded by a man as he was helping three British schoolgirls get to Syria to join the Islamic State group. Turkish authorities have said the man was working for the intelligence service of a country that is part of the anti-IS coalition, but have not publicly named the country. A Haber television says that the video it obtained was filmed in Gaziantep on Turkeyâs border with Syria. A Turkish government official, speaking on condition of anonymity because he was not authorized to comment, confirmed the authenticity of the video. (AP Photo/A Haber via APTN)
ANKARA, TURKEY - MARCH 17: A passport photo alleged to belong to 22-years-old British woman Jalila Henry and to have been used by her twin sister Jamila Henry (known and named by Turkish officials as Jaila Nadra H) as she tried to travel through Turkey to Syria to join Daesh (Islamic State of Iraq and Levant) terrorists. Jaila Nadra H was detained after an operation staged by the Turkey's Ankara Province Police Anti-terrorism department in the city's bus terminal in Ankara, Turkey on March 17, 2015. (Photo by Turkish National Police/Anadolu Agency/Getty Images)
Renu Begum, eldest sister of Shamima Begum, 15, holds her sister's photo as she is interviewed by the media at New Scotland Yard, as the relatives of three missing schoolgirls believed to have fled to Syria to join Islamic State have pleaded for them to return home, on February 22, 2015 in London, England. Police are urgently trying to trace Shamima Begum, 15, Kadiza Sultana, 16, and 15-year-old Amira Abase after they flew to Istanbul in Turkey from Gatwick Airport on Tuesday. (Photo by Laura Lean - WPA Pool/Getty Images)
In this courtroom sketch, Tairod Nathan Webster Pugh, right, a U.S. Air Force veteran and former airplane mechanic charged with attempting to join the Islamic State group in Syria, stands with his uncuffed hands behind back during his arraignment Wednesday, March 18, 2015, before Judge Nicholas Garaufis, left, in a federal courthouse in the Brooklyn borough of New York. Pugh pleaded not guilty to terrorism charges. His attorney, Michael K. Schneider, second from right, entered the plea on Pugh's behalf in the presence of Assistant US Attorneys Samuel Nitze, center, and Tiana Demas, center left. (AP Photo/Elizabeth Williams)
In this undated image taken from video released by Turkish broadcaster A Haber on Friday, March 13, 2015, a girl believed to be one of three British girls on their way to join the Islamic State Group in Syria, is seen in Turkey. A Turkish news channel released a video that it says was recorded by a man as he was helping three British schoolgirls get to Syria to join the Islamic State group. Turkish authorities have said the man was working for the intelligence service of a country that is part of the anti-IS coalition, but have not publicly named the country. A Haber television says that the video it obtained was filmed in Gaziantep on Turkeyâs border with Syria. A Turkish government official, speaking on condition of anonymity because he was not authorized to comment, confirmed the authenticity of the video. (AP Photo/A Haber via APTN)
In this courtroom drawing, defendant Akhror Saidakmetov, left; an interpreter, center; and defendant Abdurasul Hasanovich Juraboev, appear at federal court in New York on terrorism charges, Wednesday, Feb. 25, 2015. Saidakmetov and Juraboev are two of the three men arrested on charges of plotting to travel to Syria to join the Islamic State group and wage war against the U.S. (AP Photo/Jane Rosenberg)
FILE - This undated passport photo provided by the U.S. Attorney's Office in Chicago shows Mohammed Hamzah Khan. A status hearing is scheduled Tuesday, March 3, 2015, in Chicago for Khan, who is facing federal charges of trying to travel with his siblings to Syria to join the Islamic State group. FBI agents raided his family home in Bolingbrook, Ill., for a second time days before the scheduled hearing. (AP Photo/U.S. Attorneyâs Office, File)
FILE - This photo provided by the Paris Police Prefecture Friday, Jan. 9, 2015 shows Hayat Boumedienne the suspect in the kosher market attack. Turkey's foreign minister said Monday Jan.12, 2015 that Boumedienne, wife of Amedy Coulibaly, one of the perpetrators of the terrorist rampage in France last week, crossed into Syria from Turkey on Jan. 8. The Islamic State group has put out publications claiming to have an interview with the widow of the gunman who attacked a kosher supermarket and a police officer, killing five people before he died in a raid by security forces. The text interviews in French and English, published Wednesday and Thursday, did not directly name Hayat Boumeddiene nor show any images of her. It appeared to be the first confirmation from Islamic State that she had joined the group in Syria, as was widely believed after a posthumous video emerged of her husband, Amedy Coulibaly, pledging allegiance to its leader. (AP Photo/Prefecture de Police de Paris, File)
Attorney Thomas Durkin, left, talks with Shafi, and Zarine Khan, parents of Mohammed Hamzah Khan, after a federal magistrate judge put off ruling on whether the 19-year-old Khan, accused of trying to join Islamic State militants in Syria, should stay behind bars pending trial Thursday, Oct. 9, 2014, in Chicago. Khan's detention hearing on Thursday followed his arrest last week at O'Hare International Airport as he attempted to board a plane to Turkey. (AP Photo/Charles Rex Arbogast)
ANKARA, TURKEY - MARCH 17: A 22-years-old British woman, Jamila Henry (known and named by Turkish officials as Jaila Nadra H) who is alleged to have tried to travel through Turkey to Syria to join Daesh (Islamic State of Iraq and Levant) terrorists, who has been detained after an operation staged by the Turkey's Ankara Province Police Anti-terrorism department in the city's bus terminal in Ankara, Turkey on March 17, 2015. (Photo by Turkish National Police/Anadolu Agency/Getty Images)
Handout still taken from CCTV issued by the Metropolitan Police of (left to right) 15-year-old Amira Abase, Kadiza Sultana,16 and Shamima Begum,15 at Gatwick airport, before they caught their flight to Turkey. Metropolitan Police officers are in Turkey as the search continues for three missing schoolgirls believed to have fled to Syria to join Islamic State.
In the Feb. 2, 2014 photo provided by the Rock County, Wisconsin, Sheriffâs Office is Joshua Van Haften, 34, of Madison, Wisconsin. Van Haften was arrested Wednesday, April 8, 2015 at O'Hare International Airport in Chicago after returning on a flight from Turkey. He is charged in a criminal complaint with attempting to provide material support to a foreign terrorist organization. (Rock County Sheriffâs Office via AP)
Fighters from the Iraqi Imam Ali Brigade, take part in a training exercise in Iraq's central city of Najaf on March 7, 2015, ahead of joining the military operation in the city of Tikrit. Some 30,000 Iraqi security forces members and allied fighters launched an operation to retake Tikrit at the beginning of March, the largest of its kind since Islamic State (IS) group forces overran swathes of territory last June. AFP PHOTO / HAIDAR HAMDANI (Photo credit should read HAIDAR HAMDANI/AFP/Getty Images)
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American ISIS activists and sympathizers also use other social media, ranging from open forums such as Facebook, Google+ and Tumblr to more secretive messaging apps including Kik, Telegram, surespot and the dark web, the study said.
American online ISIS supporters are sufficiently active and noisy to have established themselves as "nodes," or leading voices promoting Islamic State themes, while others serve as "amplifiers," who repost materials from more prominent activists.
The study said U.S. Islamic State activists have helped craft a "unique innovation" in militant messaging. This involves creation of "shout out" accounts, which enable activists to "introduce new pro-ISIS accounts to the community and promote newly created accounts of previously suspended users, allowing them to quickly regain their pre-suspension status."
The study noted that, although American social media accounts linked to ISIS are regularly suspended, among the activists such suspensions have become a "badge of honor and a means by which an aspirant can bolster his or her legitimacy."
Operators of suspended accounts usually set up and start using a newly created account, using only a variation of the previous user name, "within hours" of most suspensions, it said.
Even though Islamic State's forerunners first emerged after the U.S. invasion of Iraq in 2003, Islamic State's "message did not exist" before the organization established itself in Syria and became involved in a civil war against the government of President Bashar al Assad, said Lorenzo Vidino, one of the study's principal authors.
Vidino cited FBI statistics indicating that U.S. authorities are currently pursuing 900 terrorism-related investigations in all 50 U.S. states. His study noted that 71 individuals have been charged by U.S. authorities with ISIS-related offenses since March 2014, with 51 of those arrests occurring in 2015.