Online social networks like Facebook or MySpace have enjoyed a formidable success in recent times which is partly due to the provision of software-platforms for the development of social applications through third-party complementors. Consequently, the study of aspects on the role and motivations of these complementors becomes increasingly important. Our empirical study contributes by revealing how the different motivations of social application developers are interrelated and how these motivations influence application developers’ effort intensity on the platform. Drawing on established motivation theories, we develop a theoretical model and test it using empirical data from Facebook application developers. PLS-based structural equation modeling demonstrated that “external rewards” and “status and job opportunity” motives were the dominating motivational drivers. Moreover, we found that external rewards undermine intrinsic motivation, while internalized motives strengthen it. Based on our findings, we discuss practical implications regarding incentive schemes and theoretical implications as starting point for further research.