Amin, 17, a former honor student at Osbourn Park High School in of Manassas, Virginia, pleaded guilty in federal court to one count of providing material support and resources to ISIS.
Over the past two years, more than 60 Americans have been charged with trying to join ISIS or are suspected of trying to support the group in some other way. In many of the cases, adults are accused of radicalizing younger Americans -- but the opposite occurred in Amin's case, as outlined in a plea agreement.
Since June 2014, Amin amassed 4,000 followers to his Twitter account, posting nearly 7,000 messages in that time, according to the plea agreement.
Using the Twitter handle @Amreekiwitness, Amin told others how to offer financial support to ISIS and hide money sent to the group, alleges the agreement, filed in U.S. District Court for the Eastern District of Virginia.
Amin's lawyer, Joseph Flood, told reporters outside a federal courthouse in Alexandria, Virginia today that Amin is "a good kid ... a pacifist" who got caught up in his desire to topple the Syrian regime that opposes ISIS, but he understands what he did was a crime and takes full responsibility.
"All of the other people who have pled guilty or who have been convicted of this crime and providing material aid to ISIS have been all adults," Flood said. "It's a very rare occasion for a child to be caught up in this. And he is a child. He takes adult responsibility for what he did, but we can't lose sight of the fact that he is a child."
Flood later added in a written statement that the actions Amin has taken responsibility for "consisted primarily of blogging on the Internet to proselytize his Muslim faith and express his views about the ongoing insurrection in Syria."
However, according to the plea agreement, Amin admitted that in September he launched an effort to radicalize 18-year-old Reza Niknejad, a fellow Virginia native. Ultimately, Amin put Niknejad in touch with an ISIS supporter overseas who could help Niknejad join ISIS, Amin bought airplane tickets for Niknejad's trip, and he drove Niknejad to Dulles International Airport in January, the plea agreement alleges.
Niknejad is believed to still be in Syria, and he has been charged with several terrorism-related offenses.
Amin, meanwhile, faces as many as 15 years in prison. He will be sentenced on Aug. 28.
ABC News' Tom Giusto and Jack Cloherty contributed to this report.