With the increased prevalence of advanced mobile devices (the so-called “smart” phones), interest has grown in mobile social ecosystems, where users not only access traditional Web-based social networks using their mobile devices, but are also able to use the context information provided by these devices to further enrich their interactions. Owing to the large variety of platforms available for smart phones, as well as the different ways that data and context information is represented, it is natural to think of middleware solutions that the developers of these systems can use while creating their applications. In this paper, we highlight the issues which should be addressed by middleware designed for mobile social ecosystems, taking into account the heterogeneity of both deployment nodes and available data, the intrinsic distributed nature of mobile social applications, as well as users' security concerns. As part of our ongoing effort to develop this middleware, we present a comprehensive model to represent mobile social ecosystems and the interactions possible in them, and show how to exploit it in a representative scenario.