1. A computer-implemented method of generating clusters of users in a social network, the social network represented as a graph of nodes and the users represented as the nodes, the method comprising: generating by a similarity processor, a matrix of nodes by: obtaining a first neighbor list for a first user and a second neighbor list for a second user in the social network; finding one or more common nodes in the first and second neighbor lists; and applying a first similarity measure based on a number of the one or more common nodes and a graph-specific decay parameter, the graph-specific decay parameter describing how a similarity score is spread out in the graph of nodes according to one or more values of the graph-specific decay parameter; forming groups by a clustering processor, the clustering processor assigning select nodes to intermediate clusters responsive to the matrix and merging select clusters together responsive to similarity thereof; and modifying the intermediate clusters by adding select nodes responsive to similarity thereof.