The MyPEEPS Mobile intervention is a novel evidence-driven intervention using mobile technology to deliver HIV prevention information. This is the first study to test the efficacy of a scaled-up, mobile version of an existing HIV prevention intervention originally developed, designed, and piloted for, a diverse group of YMSM. We used an iterative design process incorporating feedback from experts and end-users to update the user-interface and content of the MyPEEPS Mobile Intervention.