Trust is a crucial issue in online shopping environments, but it is more important in social commerce platforms due to the salient role of peer-generated contents. This article investigates the relationship between trust in social commerce and purchase intentions and describes a mechanism to explain this relationship. We propose a main and two alternative models by drawing on three concepts: social commerce information seeking, familiarity with the platform, and social presence. The models clarify the mechanisms through which trust, familiarity, social presence, and social commerce information seeking influence behavioral intentions on social commerce platforms. Findings from a survey of Facebook users indicate that trust in a social networking site (SNS) increases information seeking which in turn increases familiarity with the platform and the sense of social presence. Moreover, familiarity and social presence increase purchases intentions. Findings indicate that the main model fits the data better than the alternative ones. Theoretical and managerial implications are discussed.