In the wake of the international refugee crisis, racist attitudes are becoming more publicly evident across the European Union. Propelled by the attacks in Köln on New Year’s Eve 2015 and harsher public sentiments on immigration, vigilante gangs have emerged in various European cities. These gangs mobilize through social media networks and claim to protect citizens from alleged violent and sexual attacks by refugees. This article analyzes how racist actors use social media to mobilize and organize street politics targeting refugees/immigrants. The aim is to explore the relation between social media and anti-refugee mobilization in a time of perceived insecurity and forced migration. The study uses the vigilante network Soldiers of Odin as a specific case, looking at (1) how they communicate through social media, (2) how they are represented in the large “alternative” space of right-wing online sites, and (3) how they are represented in traditional mainstream news. Using a critical adaption of Cammaerts’ theory of “mediation opportunity structure,” the article explicates the (inverted) rationale of racist online networks. Using quantitative and qualitative content analysis, both social media content and traditional news media are examined. The results show that although racist actors succeed in utilizing many of the opportunities embedded in social media communication and protest logic, they are also subject to constraints, such as a lack of public support and negative framing in news media. The article calls for more research on the (critical) relationship between uncivil engagement and social media networks.