<p>Online purchasing behavior is often influenced by social networks. Despite the marked success of offline social networks in social commerce, academic research in this area lags behind. This study addresses this gap by examining the existence, extent and mechanisms of offline peer influence on online purchasing within a relationship-oriented culture. Integrating offline social data from a campus e-commerce platform with online purchasing data, we find that offline peers positively affect consumers’ online purchase quantity, frequency, expenditure, and category count, with this effect amplifying with stronger social ties. Unlike previous studies, informational social influence is not supported; instead, <i>guanxi</i> and <i>mianzi</i> are identified as key mechanisms. This research represents the first empirical validation of the interplay between online and offline consumer behaviors within non-Western cultures, thereby enriching the literature on consumer behaviors and contributing to understanding the exponential growth of social commerce in China.</p>