Social commerce (s-commerce) has become increasingly impactful to e-commerce and has generated potential economic benefits. With the rise of online privacy concerns, we have seen the need to explain how concerns about privacy affect consumers’ social interaction behavior and purchase decision-making on s-commerce sites. Synthesizing the privacy-trust-behavioral intention (PTB) and consumer decision-making models, this study proposes a comprehensive model by specifically refining its privacy and trust from an institutional perspective and investigating the influences of social interaction on purchase intention and actual purchase behaviors. Our results found that institutional privacy assurance positively influences institutional-based trust, which, in turn, affects online social interactions, and consequently increases the likelihood of product purchases on s-commerce sites. Theoretical development of this research contributes to both marketing and information systems disciplines in the social media era.