This research starts from an activist-centric perspective and explores how different actors interfere in activist communication in social media. We pursue this inquiry through a case study of the Blockupy action against the opening of the European Central Bank headquarters in Frankfurt am Main, Germany, on March 18, 2015. The investigation combines an ethnographic inquiry into activists’ social media tactics with a social network analysis of Twitter hashtags to explore how these tactics materialize in social media. The inquiry enhances our understanding of the consequences of activists’ use of corporate social media by identifying actors, communication, and networks. Moreover, although activists define Twitter hashtags as theirs, our research shows increasing police use of them, hindering activists’ attempts to communicate alternative perspectives.