In this paper, we describe how intrinsic motivation, extrinsic motivation, and the willingness to take risks influence the activity of Facebook and iPhone application developers. Both Facebook and Apple utilise a platform business model but differ in terms of their openness towards external development. However, in any platform business model, a platform owner must encourage peripheral contributions to strengthen its market position. In this paper, we use a questionnaire to investigate the influence of different motivation structures on participation. In particular, we seek to answer the following basic questions: (1) How do voluntary developers differ from developers who are paid by professional firms in terms of their motivation? (2) How do developers working on applications for an open platform (e.g., Facebook) differ from developers working for a rather closed platform (e.g., iPhone)? (3) How does perceived support for creativity affect the motivation of a sponsored individual? We conclude by providing managerial implications and suggesting avenues for further research.