Social media (SM) have played a critical role in recent social transformation movements and yet information systems (IS) literature has only sparsely examined the role of particular SM platforms and their affordances that facilitate such collective action, and how such affordances are appropriated for decentralised forms of collaboration and cooperation. We draw on theories of affordances and collective action to identify a range of functional SM affordances, and related SM platforms, impacting online activism in the recent social transformation movements in Egypt, based on field interviews with a variety of movement participants. We identify nine perceived affordances of SM that were instrumental during the social transformation movements. When these affordances are appropriated by movement participants, they interact with and complement each other, thereby significantly impacting mobilization for social change. Our findings provide a more nuanced perspective on the role of SM in social transformation movements and have implications for both IS and collective action theories.