Sporl-Wang,K., Krause, F., & Henkel, S. (2025)

Journal of Business Research, 186, 114991.

https://doi.org/10.1016/j.jbusres.2024.114991

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This article provides a systematic literature review and meta-analysis of social media influencer (SMI) marketing effectiveness, synthesizing findings from 93 articles and 108 studies. The authors identify 56 predictors and seven dependent constructs, categorizing them into three overarching groups: influencer characteristics (“who”), content style and scope (“what”), and communication methods (“how”). The review organizes theories into four clusters: source credibility, consumer engagement, congruence, and persuasion, highlighting theoretical overlaps and inconsistencies. A key contribution is the development of a generalized model of SMI marketing effectiveness that integrates these predictors and dependent measures.

The meta-analysis focuses on customer engagement and purchase intention, the two most frequently studied effectiveness outcomes. Results show that credibility, expertise, attractiveness, and similarity significantly drive engagement, while follower count has mixed effects—sometimes negative due to reduced authenticity. Purchase intention is similarly influenced by expertise, similarity, and trust, with micro-influencers often outperforming macro-influencers due to higher perceived authenticity. Importantly, authenticity, while often celebrated in practice, was not found to significantly predict engagement outcomes.

This study contributes by reconciling contradictions in prior findings, offering managers clearer insights into influencer selection. For example, the analysis suggests follower count is not always advantageous, and effectiveness depends on campaign goals (engagement vs. purchase). The authors emphasize the need for more quantitative, multi-theory approaches to unify fragmented insights in influencer marketing research. Ultimately, this work positions influencer effectiveness as a multifaceted construct influenced by interrelated factors, providing both scholars and practitioners with a structured framework to optimize influencer campaigns.