IntroductionYouTube vloggers may be important socialization figures, yet their influence on adolescents' health‐related behaviors and cognitions is largely untested. In this two‐study mixed‐method project, we first assessed the extent of (non)compliance to COVID‐19 regulations by vloggers on YouTube and how viewers reacted to this. Second, we experimentally assessed the effects of vlogger behavior paired with viewer evaluations on adolescents' COVID‐19‐related attitudes, intentions, and behavior.MethodsFor Study 1, we coded 240 vlogs of eight popular Dutch vloggers on YouTube recorded in the period of February 2020–March 2021. For our 2 × 2 between‐subjects experiment in Study 2, Dutch adolescents (N = 285, Mage = 12.99, SD = 1.02, 41.8% girls) were randomly assigned to conditions in which they saw vlogs showing either compliance or noncompliance to COVID‐19 regulations, and to conditions in which they saw either supportive or dismissive comments under these vlogs.ResultsStudy 1: Vloggers' noncompliance with COVID‐19 regulations was not uncommon and received relatively more viewer support than compliance, suggesting that portrayed noncompliance may be potentially influential. Study 2: Adolescents were more worried about COVID‐19 after they watched a compliant (vs. noncompliant) vlogger. Also, vlogger noncompliance decreased adolescents' perceived importance of COVID‐19 regulations and rule‐setting for adolescents who identified strongly with the vloggers they watched.ConclusionsVloggers' (non)compliance affects adolescents' COVID‐19‐related worrying, and attitudes and behavior of adolescents who identify with vloggers strongly. This seems concerning given the sometimes harmful and risky behaviors vloggers portray online but could potentially also be employed to encourage healthy behaviors.