Social TV (STV) that utilizes social media to create an interactive backchannel for video viewing increasingly attracts social audiences. This national web survey in Singapore was conducted to investigate 600 social media users with online video discussion experiences. The STV model examines the relationships and mediation effects among social constructs (i.e. perceived sociability, perceived social presence, and bridging social capital), program commitment, and program loyalty. Structural equation modeling results show that bridging social capital is positively associated with commitment and loyalty to programs. In addition, perceived social presence increases program commitment, but perceived sociability has no effect. Perceived sociability, as a predictor of social presence, and social presence itself are positive factors affecting bridging social capital. Moreover, bridging social capital significantly mediates the relationships between perceived sociability and program loyalty. Theoretical and practical implications for STV’s social constructs and program loyalty are discussed.