How do modern social movements broaden their base? Prompted by the viral video footage of George Floyd's murder, the Black Lives Matter (BLM) movement gained unprecedented scope in the spring of 2020. In this paper, we show that pandemic exposure (COVID-19 related deaths) significantly increased the take-up of social media and subsequently mobilized protesters in whiter, more affluent and suburban counties with low ex-ante probability of protesting. We exploit Super Spreader Events in the early stages of the pandemic as a source of plausibly exogenous variation at the county level and develop a novel index of social media penetration, using information from more than 45 million tweets, google searches and mobility data. We show that a one standard deviation increase in pandemic exposure increased the number of new Twitter accounts by 27% and increased protest propensity by 9 percentage points. Our results suggest that social media can be persuasive and inspire action outside of traditional coalitions.