Social media platforms such as Facebook, Twitter, and LinkedIn became mainstream at precisely the moment when universities made a renewed commitment to the social impact of their research. There are vast audiences using these services, which creates a powerful sense that the “public” with whom we are trying to engage can be accessed through them. Furthermore, they enable us to engage with their audiences in flexible and multimodal ways, which hold out the possibility of building relationships beyond traditional gatekeepers within the media. The reality of using social media for public engagement is considerably more complex than its enthusiastic reception within higher education over the last decade would seem to suggest. These are powerful tools which can be used to build relationships with external audiences, but doing so, requires a careful strategy with a clear sense of who these groups are and why they might be interested in connecting. In the absence of such a strategy, there are considerable risks attached to using social media for public engagement, such as wasting time which could be better spent on other activities and being the target of online harassment.