Abstract Advertisers typically publish in‐feed ads with two types of authorship: brand or influencer, yet little is known about the effectiveness of in‐feed ads between these two authors. In this study, we investigated the interactions and mechanisms of ad authorship (brand vs. influencer) and brand type (luxury vs. mass) on advertising effectiveness, and tested the moderating effect of upward social comparison based on the stereotype content model. A pilot study, by coding the secondary data from Most Liked WeChat Moment Ads, found that a greater proportion of luxury (vs. mass) brands were authored by brands (vs. influencers). Study 1 used eye tracking technique to identify the interactive effect of ad authorship and brand type on visual attention. Study 2 further identified perceived competence and warmth as mediators. Study 3 verified the moderating effect of upward social comparison on the above effects. This paper contributes to the theoretical literature on in‐feed advertising by showing the interactive effect of advertising authorship and brand types on advertising effectiveness. It also offers valuable insights for luxury or mass brands on strategically leveraging the brand itself or influencer for advertising.