PurposeThe objective of this study was to evaluate the effect of message frames (gain vs. loss) and sources (formal expert: a health-care professional vs. informal expert: an individual who successfully quit vaping) on the persuasiveness of TikTok videos among youth who currently use e-cigarettes. Additionally, the study examined how emotional responses and perceived message effectiveness (PME) mediate the framing effect on youth intention to quit vaping. MethodsA 2 (gain frame vs. loss frame) × 2 (formal expert vs. informal expert) factorial design experiment was conducted with 378 youth aged 13 to 18 who currently use e-cigarettes. The study measured participant's emotional responses, PME of the messages, and intention to quit vaping after the video exposure. ResultsMessages from a formal expert resulted in stronger intention to quit vaping compared to messages from an informal expert. Gain-framed messages were associated with higher PME when delivered by an informal expert, whereas loss-framed messages showed stronger effects on PME from a formal expert. Positive emotional responses and increased PME mediated the relationship between gain-framed messages and youth intention to quit vaping. DiscussionTikTok could serve as an effective tool for formal experts to promote vaping cessation among youth who use e-cigarettes. Additionally, the findings suggest that gain frames may be more influential than loss frames in promoting vaping cessation among youth, by eliciting positive emotional responses from the audience. The differential impact of message frames depending on source type indicates a nuanced interaction between content and messenger.