This paper describes the development and results of a web survey, named the Party Panel, that addresses emerging risks in nightlife settings. The survey does so by gathering the information that prevention organisations require to develop theory- and evidence-based behaviour change interventions. The survey supports the development of such interventions by mapping the determinants and sub-determinants of substance use-related behaviours among Dutch nightlife participants. The paper presents the results of the survey round which focused on highly dosed ecstasy pills, an issue which prompted public health concerns and highlighted the need to develop interventions to discourage the use of high doses of MDMA. As the authors highlight, because all Party Panel resources, data and analysis scripts are openly available, and the infrastructure is completely open-source, other organisations can use the survey results or copy the resources to their servers to set up similar web surveys. This approach allows prevention professionals to rapidly identify which sub-determinants need to be targeted in campaigns responding to emerging risks. By extension, this shows how web surveys can be valuable tools in addressing emergent risks in nightlife settings and in developing appropriate interventions based on those risks.