Exemplary embodiments relate to techniques for determining social networking or messaging user affinity and engagement coefficients (e.g., a measure of the connectedness between two people in a network). The described techniques are particularly well-suited to cases in which only limited information is available, such as when a new user joins a network and only the user's contacts list is available. The available information may be used to determine a group of existing users to which the new user is connected. Some embodiments relate to calculating scores among these existing users in order to infer an affinity for the new user to the existing users. Other embodiments involve calculating bilateral scores that reflect a degree of mutual affinity between two users.