This study examines the use of collective action frames and the mobilizing strategies on social media by LGBT communities in Taiwan to promote samesex marriage and build a supportive social consensus. Content analysis and textual analysis were conducted to analyze postings on the Facebook fan pages of four groups that support same-sex marriage, followed by in-depth interviews with 10 activists from these groups. The findings demonstrate that "diagnostic frames" were the most commonly used frames, followed by "motivational framings" and "blaming frames" The comments against same-sex marriage argued that the traditional marriage supports public interest, the function of the family, and proper parenting, whereas the postings that support same-sex marriage emphasized the importance of human rights, marriage equality, and progressive social values. In terms of mobilization, social media eliminated geographical boundaries and expanded the size of alliance networks that through the development of interpersonal links. Endorsements from social media influencers also attracted more supporters to identify with the cause of the activists. This exemplifies the unique dynamics of “social media coalition politics.” Since the social media functions as private communities as well as public platforms, it provides a field of interdiscursivity for intimate relationships to flow across the boundaries between the private and the public.