The use of social media influencers as persuasive marketing agents has become ubiquitous. However, a comprehensive understanding of their effectiveness, mechanisms, and moderation is still lacking. To address this gap, we conducted a meta-analysis of 71 papers, yielding 135 experimental studies and 571 effect sizes related to the impact of social media influencers compared to other forms of brand endorsements. Our results reveal that social media influencers significantly impact both consumer engagement and purchase intention, and they are relatively more effective than brand posts, virtual influencers, and celebrities. A meta-analytic structural equation model analyzing the influencing mechanisms suggests that social media influencers enhance consumer responses indirectly through their credibility and attractiveness. A meta-regression analysis further shows that various factors—including characteristics of the influencers, message, products, social media platforms, and followers, as well as their interaction with influencer size—moderate the effectiveness of social media influencers. Notably, our results indicate that influencer size can address some inconsistencies in previous research. For instance, small and medium-sized influencers are more effective in driving engagement, while larger influencers have greater impact on purchase intention. Our research provides novel, rich, and nuanced insights that can help managers with decisions such as: (a) when to choose influencers over alternatives, and (b) how to optimize their use.

使用社交媒体影响者作为有说服力的营销代理已经变得无处不在。然而，仍然缺乏对它们的有效性、机制和调节性的全面了解。为了解决这一差距，我们对 71 篇论文进行了荟萃分析，产生了 135 项实验研究和 571 个效应大小，与社交媒体影响者的影响相比，与其他形式的品牌代言相比。我们的结果表明，社交媒体影响者显着影响消费者参与度和购买意愿，并且他们比品牌帖子、虚拟影响者和名人相对更有效。分析影响机制的元分析结构方程模型表明，社交媒体影响者通过他们的可信度和吸引力间接增强消费者的反应。元回归分析进一步表明，各种因素——包括影响者的特征、消息、产品、社交媒体平台和追随者，以及他们与影响者规模的互动——调节了社交媒体影响者的有效性。值得注意的是，我们的结果表明，影响者规模可以解决以前研究中的一些不一致问题。例如，中小型影响者在推动参与度方面更有效，而较大的影响者对购买意愿的影响更大。我们的研究提供了新颖、丰富和细致的见解，可以帮助管理者做出决策，例如：（a） 何时选择影响者而不是替代方案，以及 （b） 如何优化它们的使用。