In an effort to address the physical inactivity crisis among adolescents, the present study will examine the efficacy of using an already established Web-based social networking platform (i.e., Facebook) to deliver a physical activity intervention to adolescents. The primary objectives of this trial are to 1) test the efficacy of a social media-delivered physical activity program for increasing lifestyle physical activity in adolescents, and 2) determine the effectiveness of a physical activity intervention based on social cognitive principles in comparison to a simple information-based physical activity condition. Additional objectives include an examination of how program participation may influence psychosocial health and how these changes affect physical activity patterns in youth.