This paper presents the development and evaluation of a QoSN (standing for Quality of Social Network) model for social networks populated with Web services. These Web services are given the opportunity to select the networks in which they would like to sign in taking into account their concerns (in fact their providers' concerns) like better protection to their details and better exposure to potential users. To support Web services selection the QoSN model is built upon four criteria including robustness, trust, fairness, and traceability. The computa- tion of these criteria uses a cryptographic technique known as Secure Multi-Party Computation (SMC). Different experiments showing how the networks react to Web services' actions (e.g., attack, join, and kick out) are also presented in the paper.