Influencer advertising on Instagram: product-influencer fit and number of followers affect advertising outcomes and influencer evaluations via credibility and identification

Social media influencers are increasingly employed as product endorsers, and a growing body of academic research confirms that influencers are an effective advertising instrument. However, more research is needed on the specific influencer characteristics driving this success, and the processes responsible for these effects. In this study, we investigated to what extent product-influencer fit and number of followers interact in contributing to positive advertising outcomes and influencer evaluations. Moreover, we investigated to what extent perceived credibility of the influencer and identification with the influencer mediate these relationships. We conducted a 2 (poor vs. good product-influencer fit) X 2 (moderate vs. high number of followers) between-subjects experiment among 432 Dutch Instagram users. Participants were exposed to Instagram posts of health and fitness influencers who endorsed either a protein shake (good-fit) or ice cream (poor-fit). Results showed that fit and number of followers seem to work in tandem: although influencers with a high number of followers are liked more, and their endorsements result in a more positive attitude toward both the ad and product, and a greater likelihood to buy the advertised product as compared to influencers with a moderate number of followers, the endorsed product should fit the influencer's self-branded image for these positive effects to occur. Moreover, effects were all mediated by perceived credibility and identification, which appear to be important drivers of influencer endorsement effects. Together, our findings contribute to a growing body of knowledge on the processes driving audience responses to influencer marketing, and provide clear guidelines for practitioners.