This study [HOPE: Harnessing Online Peer Education] seeks to determine the efficacy of using online social networks to scale peer community leader models to increase HIV prevention within African-American and Latino men who have sex with men. The peer community leader model, which teaches community popular opinion leaders about how to disseminate behavior changes messages throughout the community, has been proven to increase HIV prevention behaviors. Social networks such as Facebook.com may be a cost-effective platform for scaling these models. Primarily upper middle-class White populations used the Internet in its early years, however, Internet use within African-American and Latino households has recently increased dramatically, especially on online social networks such as Facebook.com. People using the Internet may be at the highest risk for contracting HIV and are using novel Internet approaches to find sex partners, such as through online social networks. This is the first study to examine the effectiveness of the HOPE social media intervention to increase HIV testing among at-risk groups in the United States.