This study provides an empirical account of how an online community has employed social media to mobilize people for a political goal. The case explored is a Twitter-based community in South Korea that calls for the elimination of a conservative national daily newspaper and whose activism is contextualized in the political history of Korea. Based on the mixed-method approach, the research results suggest that the role of the group organizer as an information provider and coordinator contributed to the sustainability of the group, and that group members formed a collective identity through the framing process of discourse. In addition, massive "retweeting" and "culture jamming" tactics were found to be strategically employed to enhance group solidarity, to broaden the base of support, and to crystallize involvement into political acts with other offline actions. Rather than decaying to an echo chamber or "slacktivism", the online community seemed to demonstrate a new form of collective activism through the mediation of technology in everyday life.