Rapid and innovative advances in participative Internet communications, referred to as “social media,” offer opportunities for modifying health behavior. Social media let users choose to be either anonymous or identified. People of all demographics are adopting these technologies whether on their computers or through mobile devices, and they are increasingly using these social media for health-related issues. Although social media have considerable potential as tools for health promotion and education, these media, like traditional health promotion media, require careful application and may not always achieve their desired outcomes. This article summarizes current evidence and understanding of using social media for health promotion. More important, it discusses the need for evaluating the effectiveness of various forms of social media and incorporating outcomes research and theory in the design of health promotion programs for social media.