BackgroundHomeless and unstably housed (H/UH) youth are disproportionately affected by sexual health issues, including human immunodeficiency virus/sexually transmitted diseases, teen pregnancy, and dating violence, and are at a higher risk for poor mental health and underutilization of services. Research suggests that linking health care to H/UH adolescents might help improve their continuity of care, with most preferring to access health care information via the Internet. YTH StreetConnect is a dual-purpose mobile app that helps H/UH youth access health and vital services in Santa Clara County, CA, USA. We developed YTH StreetConnect PRO in parallel with the youth app as a companion tablet app for providers who serve H/UH youth.ObjectiveThe objective of our study was to develop a mobile app to support H/UH youth and their providers in accessing health and vital resources, and to conduct usability and feasibility testing of the app among H/UH youth and technical consultants with local expertise in serving H/UH youth.MethodsFormative research included a literature review on H/UH youths’ mobile phone and Internet usage. In January 2015, we conducted interviews with medical and service providers of H/UH youth. Usability and feasibility testing were done with target audiences. Additionally, we conducted focus groups with youth regarding the app’s youth friendliness, accessibility, and usefulness.ResultsH/UH youth and their providers noted the app’s functionality, youth friendliness, and resources. Usability testing proposed improvements to the app, including visual updates to the user interface, map icons, new underrepresented resource categories, and the addition of a peer rating system. Limitations included a small sample size among H/UH youth and providers and a single site for the study (Santa Clara County, CA), making the findings ungeneralizable to the US population.ConclusionsYTH StreetConnect is a promising way to increase service utilization, provide referral access, and share resources among H/UH youth and providers. Input from H/UH youth and providers offers insights on how to improve future models of YTH StreetConnect and similar programs that assist H/UH youth.