According to this article by Adam Brodsky, there are essentially no known cases in which American Muslim groups have helped U.S. authorities stop terrorist plots: "I know of no investigations" in which Muslims have been helpful, Rep. Peter King (R-LI), the ranking member of the House Homeland Security Committee, tells me. He says law-enforcement and counterterror officials invariably tell him Muslim cooperation doesn't exist. Sometimes agents say they're met with hostility."
Given that many prominent U.S. Muslim organizations are connected to the Muslim Brotherhood, their lack of cooperation isn't surprising. But it is chilling. Even more chilling is the lack of cooperation by Muslims who don't belong to such organizations.