Binge drinking is an important global health issue that results in a range of health and social harms. Mobile technology's portability and connectivity can be used in-situ to encourage the practice of monitoring and moderating alcohol use. Social networking services, if used among peer-support networks to promote responsible drinking, could be effective in moderating alcohol consumption. In this article, the authors describe the design of a novel mobile social networking tool to facilitate responsible drinking among young women. They also present reports from two focus group studies that examined the design of functionalities prior to use and onsite usability. Their results confirm the design's usability and the proposed functionalities' potential usefulness. Participants perceived the tool as providing easy-to-use counting and facilitation of peer supports to reduce risks during drinking sessions.