How Social Media Marketing Drives Purchase Intention in Fast Fashion: The Distinct Mediating Roles of Brand Trust and Consumer Engagement

While social media marketing (SMM) is widely used by fast fashion brands, the psychological and behavioral mechanisms through which it influences consumers’ purchase intention remain underexplored. Based on the stimulus–organism–response (S-O-R) theory, this study constructs a dual-mediation model to examine how three SMM dimensions—content quality, interactivity, and promotional activities—affect purchase intention via brand trust (a cognitive pathway) and consumer engagement (a behavioral pathway). A quantitative survey of 200 fast fashion consumers was analyzed using regression and Sobel tests. Results show that all three SMM dimensions positively affect purchase intention, with interactivity exerting the strongest direct effect. Brand trust partially mediates the effect of interactivity, whereas consumer engagement mediates both interactivity and promotional activities. Notably, content quality does not significantly influence consumer engagement, suggesting it may serve as a baseline expectation rather than an engagement trigger in fast fashion. These findings extend S-O-R theory by differentiating two parallel mediating pathways and offer actionable guidance for fast fashion brands seeking to optimize SMM resource allocation.