Background Latinx families are among the highest users of smartphones, yet few health-focused Web programs have been developed for this audience. Parent-based smartphone apps designed for Latinx families may help increase access to evidence-informed parenting programming and ultimately reduce health disparities among children and adolescents. To maximize uptake of such apps, the Center for eHealth Research and Disease Management (CeHRes) Roadmap for electronic health (eHealth) development recommends 5 phases of development: (1) contextual inquiry, (2) value specification, (3) design, (4) operationalization, and (5) evaluation. Objective Guided by the CeHRes Roadmap, our objective was to apply a community-based participatory research (CBPR) approach to mobile app development. We present a formative evaluation to inform the design of an eHealth mobile app for Latinx parents of adolescents based on a face-to-face parenting program, Padres Informados/Jovenes Preparados (PIJP). Methods Community participants in the process included Latinx parents and stakeholders. We conducted a parent survey (N=115) and interviews (N=20) to understand the context and obtain feedback on a mockup and prototype of the app, facilitator workshops to streamline content, and stakeholder interviews (N=4) to discuss values and app requirements. Results We report results from the first 3 phases of the CeHRes Roadmap. In the survey, 96.5% (111/115) of parents reported they had access to a cell phone, 85.6% (89/104) reported they would use a parenting app in the next month if they had access, and 80.2% (89/111) reported intentions to use a stress reduction app. Parents reported that setting goals about parenting and tracking those goals were important potential features of an app. In logistic regression analyses, technology attitudes and barriers were not related to parent’s intentions to use a parenting mobile app (95% CI 0.51-1.17 and 95% CI 0.28-2.12, respectively). Qualitative interviews confirmed Latinx parents’ technology engagement and desire for education and child development information online. Stakeholder interviews identified 3 community values: familism, the promotion of adolescent health, and delivery of economic value. Community stakeholders participated in defining the mobile app requirements. On the basis of community and parent input, the mobile app prototype was designed with 3 sections: (1) 8 modules of video-based parenting skills instruction with content from the face-to-face PIJP program, (2) breath rate information from a wearable device to support awareness of stress levels that could affect parenting, and (3) goal setting and tracking capacities. Conclusions The findings of this study highlight the utility of an iterative, participatory design process. The CBPR approach and community collaboration enhanced the CeHRes Roadmap by promoting power sharing, facilitating recruitment, and building trust among community members. Experiences applying community research to the initial 3 phases of the CeHRes Roadmap in a Latinx community are discussed, along with plans for the 2 final phases.