Obesity is a chronic condition that influences the quality of life of patients and families while increasing the economic burden for the world population. Multidisciplinary prevention programs are crucial to address it, allowing an early introduction of healthy behaviors into daily habits. Mobile health interventions provide adequate support for these programs, especially considering the gamification techniques used to promote users’ engagement. TeenPower is a multidisciplinary mHealth intervention program conducted in Portugal during 2018 to empower adolescents, promoting healthy behaviors while preventing obesity. An agile software development process was applied to the development of the digital platform that holds a web-based application and a mobile application. We also propose a model for future developments based on the user-centered design approach adopted for this development and the assessment conducted in each phase. The user-centered design approach model proposed has three distinct phases: (1) design study; (2) pre-production usability tests; and (3) post-production data. Phase 1 allowed us to obtain the high-fidelity version of the graphical user interfaces (n = 5). Phase 2 showed a task completion success rate of 100% (n = 5). Phase 3 was derived from statistical analysis of the usage of the platform by real end users (n = 90). We achieved an average retention rate of 35% (31 out of 90 participants). Each technique has provided input for the continuous design and improvement of the platform. This allowed the creation of a tailored platform that could meet users’ expectations. Nevertheless, the retention rate decreased significantly over a short period of time, revealing the need for further work in the improvement of the gamification experience.