There are several million Americans who worship as Muslims. In the last decade, exactly 161 of them have been suspected of being involved in terrorist activity. The primary source of reporting these potential terrorists plots to authorities has been American Muslims, themselves.
An contrary to certain persistent rumors, American Muslims have been proactive in cooperating with law enforcement agencies, and in working proactively to end radicalism in their communities.
Here are two specific reports with the details:
64 Pages, PDF; Duke University, 2010
8 Pages, PDF; Duke University, 2011