Purpose This paper aims to explore whether, how and when influencers’ value co-creation behavior in a post – influencers investing operant resources to enhance the value gained from using the product – shapes consumers’ responses toward an influencer’s recommendation. Based on value co-creation theory and consumer inference, this paper proposes that consumers infer influencers have more expertise with and more favorable attitude toward the product from value co-creation. Consequently, such behavior can foster consumer engagement and favorable attitude toward the recommended product. Design/methodology/approach The authors collected real-world data and conducted four sets of experimental studies. In the experimental studies, the presence of an influencer’s value co-creation behavior (i.e. co-creation vs. control) was manipulated to test the causal effect and mechanisms of co-creation on engagement and product attitude. Findings Results show that influencers’ value co-creation behavior positively affects consumers’ engagement and attitudes toward the product. These effects are driven by perceived influencer’s expertise with and favorability toward the product (Studies 1 and 2). Co-creating utilitarian value is more effective than co-creating hedonic value (Studies 3A and 3B). In addition, influencers with a larger number of followers benefit more from co-creation behavior than those with fewer followers (Study 4). Research limitations/implications This research adds to the literature on value co-creation by investigating how, why and when influencers’ value co-creation enhances consumer responses to the post. Our investigation concretizes value co-creation behavior in the context of influencer marketing and demonstrates its signaling effect with nuanced role of value type in shaping the effect. The findings provide a novel cue that influencers can use to enhance consumer responses to their posts. Practical implications Brands should encourage influencers to focus on value-in-use co-creation when promoting their products. While emphasizing value co-creation in influencer partnership, brands should also carefully consider the type and size of influencers they collaborate with based on the nature of their products and target audience. The research findings also provide practical implications for influencers, offering guidance on how they can optimize their content creation strategies and enhance their effectiveness in influencer marketing collaborations. Originality/value This research enriches understanding of value co-creation in the context of influencer marketing and the role of content specifics in influencers’ posts. The findings provide a novel cue that influencers can use to enhance consumer responses to their posts.