Islamic State supporters used at least 46,000 Twitter accounts in late 2014, according to a report by the Brookings Institution, a Washington-based research organization.
The Brookings analysis found that typical backers of the militants were located within the group's territories in Iraq and Syria.
The report says the accounts were used from September through December, though not all were active at the same time.
Much of Islamic State's social media success, said the report, can be attributed to between 500 and 2,000 "hyperactive users" — accounts "which tweet in concentrated bursts of high volume."
"Social media companies and the U.S. government must work together to devise appropriate responses to extremism on social media," said the executive summary of the 68-page report.
Contrary to arguments that account suspensions do not work, Brookings said the practice does "have concrete effects in limiting the reach and scope of ISIS activities on social media."
"Although discussions of this issue often frame government intervention as an infringement on free speech, in reality, social media companies currently regulate speech on their platforms without oversight or disclosures of how suspensions are applied," said the authors.
Islamic State's use of social media has included its distribution of disturbing videos and images showing the beheadings of Western journalists and aid workers captured by the group. The graphic propaganda took a turn early last month with a video of a Jordanian hostage — an air force pilot — being burned alive.