In 2011, Chile experienced two massive protest movements - one against the cost and quality of public education and another against the construction of power plants in Patagonia. This represented a unique opportunity to analyse and compare how Facebook and Twitter use were related to street demonstrations. Using a probabilistic face-to-face survey among urban youth (18-29 years old) conducted shortly after the protests, this study revealed a positive relationship between the use of social media and participation in both social movements, even controlling for other relevant variables (e.g. political interest, ideology and trust). The theoretical and methodological implications of these findings are discussed in this article.