Social media influencers are online content creators who seek audience support, form relationships with their audiences, and shape audience interests, opinions, and behavior. Not only is the influencer economy a cultural market in its own right, but it is also increasingly shaping other cultural industries as influencers serve as cultural gatekeepers who filter cultural products for their audiences (Hirsch, 1972). As social media influencers become powerful gatekeepers and producers, the relational nature of their activities and performance is reshaping norms in cultural industries overall. Lay audiences gain more influence and agency as their evaluations and support are critical for influencer survival and success. Then how has the evaluative landscape in cultural industries changed, and what are the broader social implications of these changes? In this dissertation, I outline the rise of social media influencers both as gatekeepers and producers in cultural markets and argue that scholarship in management and sociology must examine the unique ways in which these influencers’ activities differ from their predecessors’. Chapter 1 defines social media influencers and describes their activities and market dynamics by comparing and contrasting them to their traditional counterparts. Chapter 2 examines the relationship between influencer-audience relational interactions and performance outcomes, focusing on influencers’ role as cultural gatekeepers. Chapter 3 looks at the effects of race and race-based social movements on influencer-audience interactions, highlighting influencers’ role as cultural producers. In all three chapters, the focus is on the sociological theory of relational work, which is the process through which economic actors balance the transactional and social components of their relationships (Zelizer, 2012; Bandelj, 2020). Social media influencers serve as an ideal type to demonstrate how relational work contributes to market value and performance, given the tight balance between their relational and transactional activities. I use mixed quantitative and qualitative methods to analyze channel-, video-, and comment-level data on 1,167 BookTubers (YouTube influencers who evaluate books). I find that social media influencers indeed serve as trusted gatekeepers for their audiences, and that audiences demand not only evaluative content, but also intimate relationships with influencers. Influencers use audience interactions as relational work efforts to build trusting relationships with audiences and gain their support, but this effect is moderated by the perceived trustworthiness of the influencer. The effectiveness of influencer relational work also varies by race, and relational work thus reproduces racialized logics that underlie cultural markets. In sum, this dissertation not only highlights the rise of an important new market actor, but also contributes to theories on how relational work shapes and is shaped by inequality.