Social commerce, an integration of social media into e-commerce, is on the rise and serves as an important search and purchase channel for consumers. However, little is known about how social commerce differs from traditional e-commerce in stimulating consumer purchase behavior. Drawing on the theory of perceived behavioral control, this study contributes to the literature by proposing a theoretical framework that links the pre-purchase search channel (i.e., social commerce vs traditional e-commerce) to purchase quantity. To test hypotheses, we utilize a large sample consisting of 279,098 pre-purchase click events of 6,721 products purchased by 247,069 consumers in March 2018. The empirical results suggest that purchase quantity is lower when a consumer searches through a social commerce channel compared to a traditional e-commerce channel. We also examine the moderation effects of the characteristics of consumers and products. To show the generalizability of our main finding, we further conduct qualitative interviews with 20 participants from 12 countries. Our conclusions provide practitioners with critical managerial implications.