D2D communications is one of the key technologies to enable aggressive spatial frequency reuse in future evolution of cellular systems. While the standardization efforts are far from their final stage there is clear understanding that security is one of the major concerns for proximity services. This is especially the case when one or more communicating stations in a logical cluster do not have an active connection to the serving base station. In this paper we propose a solution for secure throughput optimized communications in D2D-assisted cellular system. In order to provide additional throughput, a game-theoretic optimization approach is considered by taking into account social relationships and devices proximity. The proposed solution is agnostic to the chosen D2D communications technology (i.e., WiFi or LTE) and suitable for any possible cluster combination in full and partial cellular coverage. Performance evaluation of the proposed security framework show that social proximity information available at the D2D devices may substantially improves the system performance in term of throughput with respect to the standard security procedures. Finally, for sake of completeness, the effect of mobility for the reference scenario is evaluated.