The pursuit of greater research 'impact' has become embedded within Higher Education, through links to perceived value for money, and reified through institutional auditing processes. Academics are frequently encouraged to use social media to facilitate public engagement and enhance research impact, as it offers the potential to connect with more diverse, non-academic audiences. However, little is known about the relationship between the use of social media and academics' own perceptions of research impact and public engagement in practice. In this paper, an analysis of text responses from a survey of academics (n = 107) is presented. This includes what academics perceive to be examples of high-impact interactions through social media, and how this is mediated by different platforms. The findings have practical implications for social media training for academics and also suggest that institutional definitions of research impact may not account for the range of scholarly engagement social media platforms can facilitate.