PROJECT SUMMARY/ABSTRACT Electronic cigarette (e-cigarette) use ("vaping") has increased alarmingly in adolescents in the past years. As adolescents are a coveted marketing target of the e-cigarette industry, and e-cigarette use has risen dramatically in recent years, adolescent vaping has become a serious and urgent public health issue to be addressed. Social media is the most popular media among adolescents, and therefore holds promise to become an ideal platform to deliver vaping cessation interventions to adolescents. However, health behavior change interventions delivered on social media face a common challenge: low retention and reducing engagement as interventions unfold. Retention and engagement are essential to successful social media interventions. Literature informs social media interventions that Integrating peer mentoring into interventions may be a potential solution, because it can provide the human support and peer modelling that people need to overcome difficulties with health behavior change, and it can cultivate the accountability that can facilitate adherence and engagement. However, though shown to be promising in many health promotion projects, including smoking cessation interventions, peer mentoring has not been leveraged in social media interventions. This study would be the first to explore the application of peer mentoring into social media interventions to address adolescent vaping. The overall goal of the proposed research is to develop a feasible and acceptable peer mentoring system for adolescent vaping interventions delivered on social media. To achieve this goal, based on an existing peer mentoring text-based program for adult smoking cessation and the infrastructure of an ongoing randomized trial of an adolescent vaping intervention delivered via Instagram, this study will accomplish two specific aims: (1) develop a peer mentoring system for social media interventions for adolescent vapers, and (2) pilot test the feasibility and acceptability of the peer mentoring system in a social media-based vaping cessation intervention with adolescent vapers. In sum, combined with the advantages of social media interventions which are not confined to geography and logistics of in-person interventions, peer mentored social media interventions have the potential to significantly improve participant engagement and retention and to further enhance intervention efficacy to help adolescents quit vaping. This research may also shed light on other health behavior change interventions delivered on social media. The proposed study provides important experience and preliminary data for Dr. Lyu’s next NIH K research career development award application and facilitates her development into an independent investigator in the field of public health devoted to developing novel and evidence-based effective tobacco control interventions to help people quit tobacco consumption.