The rapidly increasing prevalence of obesity is a phenomenon often referred to as the "obesity epidemic". Literature suggests social networks to be one of the most important dimension of people's social environment that may enable or constrain the adoption of health-promoting behaviors. Given that online social networks are becoming more important in people's daily lives, this research in progress incorporated a design science research methodology for designing a Health 2.0 Facebook application to investigate the relationship of online social networks and health-related behaviors in the context of obesity. Specifically, the application enables medical and healthcare practitioners to (1) understand the effect of obesity propagation in online social networks; (2) identify potential online intervention strategies to disseminate health-related information to the right group of people and (3) to offer services fostering positive health-related behaviours or to promote behaviour change advice.