This article develops and tests a model to explain web-based and mobile devices usage by citizens to interact with their local government. By employing literature from diverse fields of information systems research, the authors derive an integrated model that investigates citizen participation on a city improvement platform. The model proposes three overall influences on platform activity: technological influences (perceived ease of use, perceived usefulness), motivational influences (intrinsic motivation and prosocial motivation), and socio-demographic influences (gender, age, education), and is tested among two groups of users (i.e. web page and mobile app users). Empirical results show that platform activity of both web and mobile users is mainly driven by intrinsic and prosocial motivation. Whereas perceived usefulness is positively associated with platform behavior of web users, TAM variables have not effect on mobile users’ activity. While gender and age play a role regarding web activity, age and education influence mobile participation.