The persuasive power of social media influencers: the effects of product congruence, altruistic motivation and storytelling

Purpose As social media becomes increasingly integral to digital marketing, brands frequently collaborate with influencers who integrate product endorsements into their online content. While prior research highlights the importance of influencer-product congruence, less is known about how communication format and sponsorship disclosure jointly shape consumer responses. This study examines how influencer-product congruence influences consumers' purchase intentions through perceived altruistic motivation and how this relationship is moderated by post type and sponsorship disclosure. Design/methodology/approach Three empirical studies were conducted using online samples of social media users recruited through the Credamo platform in China (N = 735). Study 1 used a survey-based design to test the mediating role of perceived altruistic motivation. Study 2 employed a 2 × 2 experimental design to examine the moderating role of post type (storytelling vs informational). Study 3 extended the model using a 2 × 2 × 2 experimental design to investigate the additional moderating role of sponsorship disclosure. Findings The results show that influencer-product congruence increases consumers' purchase intentions, and this relationship is partially mediated by perceived altruistic motivation. Storytelling posts strengthen the positive effect of congruence on purchase intention, whereas informational posts become less persuasive when sponsorship disclosure is present. Originality/value This study contributes to influencer marketing research by integrating influencer-product congruence, narrative communication and sponsorship disclosure within a unified framework. By identifying perceived altruistic motivation as an underlying mechanism and demonstrating the interaction effects of post type and disclosure, the findings provide both theoretical insights and practical guidance for designing more effective influencer marketing campaigns.