Emerging adult gay, bisexual, and same-sex attracted men (EAGBM; ages 18-24) are vulnerable to unique sexuality-related stressors that increase risk for suicidal ideation and behaviors. Unique risk factors predict suicidal ideation and attempts in EAGBM, yet there are few targeted interventions to reduce suicide risk in EAGBM by improving social support, coping, and positive affect. While evidence-based interventions like the safety planning intervention (SPI) significantly reduce suicide risk, research indicates that individuals struggle to use the safety plan in suicidal crises. Thus, we propose to examine a mobile application (Supporting Transitions to Adulthood and Reducing Suicide; STARS) that leverages peer mentoring and support to ensure that EAGBM can implement their safety plan in times of crisis. We will use the ADAPT-ITT Model to adapt an online life skills intervention to reduce suicidal ideation and behaviors among EAGBM. STARS will include suicide prevention content, including safety planning and targeting positive affect, consider cultural factors that may impact the efficacy of safety planning for EAGBM (e.g., access to LGBTQ+ safe spaces), and include supports that promote use of a suicide safety plan. STARS peer mentors will also provide social support, reduce the impact of discrimination, connect youth to safe spaces, and help them overcome obstacles to use their safety plan. Guided by the RE-AIM implementation science framework, we then will pilot test STARS using a Type 1 Effectiveness- Implementation Hybrid Design in a racially/ethnically diverse sample of EAGBM (n=60) living in Philadelphia who report past-month suicidal ideation. Participants will be randomized to an in-person brief, evidence-based safety planning protocol (Control arm) or to safety planning plus access to STARS (Intervention arm). We will follow participants over six months, with evaluations at 2, 4, and 6 months. Consistent with our Type 1 design, we will prioritize preliminary efficacy outcomes (suicidal ideation and behavior) and hypothesized mechanisms of change (coping with discrimination, social support, positive affect) needed to estimate critical parameters for a future trial as our primary outcomes. We also will assess key implementation indicators in both arms (participants: willingness and adoption of safety plan intervention or STARS; staff: experiences adapting and delivering the program) as secondary outcomes. Our Specific Aims are (1) To conduct a systematic suicide prevention adaptation of iREACH (“STARS”) that incorporates safety planning content and targets coping, social support, and positive affect using the ADAPT-ITT framework; (2) To examine preliminary efficacy (suicidal ideation and behaviors) and mechanisms of action of STARS, relative to our control condition (safety planning protocol alone), using a prospective RCT design, and (3) using RE-AIM metrics, to examine whether STARS has preliminary evidence for impacting intervention ...