Requirements engineering (RE) represents a decisive success factor in software development. The novel approach of crowd-based RE seeks to overcome shortcomings of traditional RE practices such as the resource intensiveness and selection bias of stakeholder workshops or interviews. Two streams of research on crowd-based RE can be observed in literature: data-driven approaches that extract requirements from user feedback or analytics data and collaborative approaches in which requirements are collectively developed by a crowd of software users. As yet, research surveying the state of crowd-based RE does not put particular emphasis on collaborative approaches, despite collaborative crowdsourcing being particularly suited for joint ideation and complex problem-solving tasks. Addressing this gap, we conduct a structured literature review to identify the RE activities supported by collaborative crowd-based approaches. Our research provides a systematic overview of the domain of collaborative crowd-based RE and guides researchers and practitioners in increasing user involvement in RE
