Suicide is the second leading cause of death among adolescents, and youth who are cyberbullied are twice as likely to exhibit suicidal thoughts and behaviors as those who are not cyberbullied. Cyberbullying (CB) is strongly associated with suicidal ideation, a phenomenon known to fluctuate rapidly, which suggests need to intervene proximally to instances of CB to reduce suicide risk. There is public health need to reduce suicide risk among cyberbullied adolescents, especially underserved adolescents (i.e., youth from minority backgrounds) who face higher rates of CB and suicidal thoughts and behavior. Yet, current interventions are limited in their capacity to meet the needs of underserved youth and to intervene in moments of high vulnerability. The purpose of this Mentored Patient-Oriented Career Development Award (K23) is to provide the applicant, a behavioral health scientist and clinical social worker, with the skills necessary to bridge the gap between CB intervention and suicide prevention with stakeholder-informed and empirically driven digital interventions for adolescents. To accomplish this long-term goal, a multidisciplinary training plan will provide the applicant with expertise in: (1) design, conduct, and analysis of online clinical trials; (2) theory, research, and methods of adolescent CB assessment and intervention; and (3) methods of enhancing underserved adolescents’ utilization of digital interventions using human centered design (HCD) and brief motivational interventions. The applicant will receive mentoring in a strong multidisciplinary environment with accomplished experts in the fields of adolescent suicide prevention, CB research, HCD, and online clinical trials. Formal training and coursework will advance training in clinical trial design and conduct (ethics and social media- based recruitment), and analysis (mediation and moderation analysis and evaluation of machine learning [ML] models for clinical trials), CB research, and methods for enhancing engagement (HCD and motivational interviewing). A complementary research plan will focus on development and testing of imHere4U, a just-in- time, suicide prevention intervention for cyberbullied adolescents. Based on pilot data suggesting acceptability of imHere4U among cyberbullied youth, parents, and professionals, we propose three aims. Aim 1: Cyberbullied adolescents (N=20; >35% underserved) will participate in iterative design to optimize a digital product for their needs. Aim 2: Recently cyberbullied adolescents (N=80; >35% underserved) will participate in an online RCT testing imHere4U plus Questionnaires of online interactions vs. Questionnaires alone. Aim 3: We will examine the feasibility of using a ML algorithm to deliver feedback to adolescents on their supportive and bullying online interactions. This trial will test the feasibility and preliminary efficacy of imHere4U, essential data for a subsequent R01 application to test imHere4U’s efficacy within a larger sam...