Do new communication technologies, such as social media, alleviate the collective action problem? This paper provides evidence that penetration of VK, the dominant Russian online social network, led to more protest activity during a wave of protests in Russia in 2011. As a source of exogenous variation in network penetration, we use the information on the city of origin of the students who studied with the founder of VK, controlling for the city of origin of the students who studied at the same university several years earlier or later. We find that a 10% increase in VK penetration increased the probability of a protest by 4.6% and the number of protesters by 19%. Additional results suggest that social media induced protest activity by reducing the costs of coordination rather than by spreading information critical of the government. We observe that VK penetration increased pro-governmental support, with no evidence of increased polarization. We also find that cities with higher fractionalization of network users between VK and Facebook experienced fewer protests, and the effect of VK on protests exhibits threshold behavior.