The widespread availability and use of social media has drastically altered disaster response in the last few years. Although a considerable amount of empirical research addresses social phenomena enabled by social media in response to disasters, the field still lacks a clear-cut knowledge base. We conduct a systematic literature review to illustrate the state of the art with respect to collective behaviour in social media in disaster situations. We find that social media have the potential to alter well-known patterns of collective behaviour, such as the distribution of activities undertaken by different types of actors over the disaster management lifecycle. Social media furthermore loosen the structural relationships between actors as they facilitate addressing wider audiences and enable communication to unspecified receivers. We conclude that future research should specifically address the causal relationship between collective behaviour in social media and the characteristics of disasters. Furthermore, research should pay particular attention to adapting existing theories and frameworks to, and developing new theoretical approaches for, the emerging digital world.