In this paper, we propose a model for an open framework that allows mobile users to create and to participate to context-aware virtual communities. The model we propose and implement is a generic data model fully compliant with the semantic web data model RDF. This model is suited to let mobile end-users use, create and customize virtual communities. We combine fundamentals for a decentralized semantic web social network with context-aware virtual communities and services. Smart cities scenarios are typically targeted with this approach. It can be implemented in places like metro stations, museums, squares, cinemas, etc. to provide ad hoc context-aware information services to mobile users.