A better understanding of the transition from child to adult community mental health services is important given the high rates of service drop-out. Conducting longitudinal research is challenging during a major service provider change. Developmentally-typical transition-to-adulthood instability can deter study engagement. This study examines the efficacy of creative technology-based strategies to recruit and engage adolescents and young adults (AYA) with serious mental health diagnoses in a qualitative study during their transition from child to adult services. Participants were recruited from one agency to complete three in-depth qualitative interviews and monthly surveys exploring mental health service experiences over 12-months. Participants received a smartphone and data plan for 6-months at initial interview, $50 at 6-month interview and $55 at 12-month interview. Four research assistants used a shared Google Voice account to text monthly online surveys and to communicate with participants. 19 participants enrolled; 74% remained enrolled across the 12-months. Smartphones and data plans were not effective in recruiting nor sustaining study engagement for most participants. Participants preferred a mix of texting and phone calls to prompt study engagement; 60% of online surveys were completed. Unanticipated participant-researcher communication outside of research scope suggests that the formation of strong relationships and additional support during this transitional time is critical for sustained study engagement. Study findings have practical implications for social work longitudinal research design and effective study implementation. Future social work research is warranted on innovative strategies to boost study and service engagement among AYA with serious co-occurring mental health and developmental instability.