1. A method, comprising: reducing, by a system comprising a processor, a sampling size of a total population of social network users of an on-line social network based on a comparison of seed information to a population of the social network users to obtain a reduced population of social network users of the on-line network; sampling, by the system, the reduced population of the social network users utilizing a Metropolized randomized walk algorithm to obtain first sampled social network users; sampling, by the system, the reduced population of the social network users utilizing a crawl algorithm that includes non-active users of the on-line social network to obtain second sampled social network users; generating, by the system, a social network graph based on the first sampled social network users and the second sampled social network users, wherein the social network graph comprises an arrangement of the first sampled social network users and the second social network users based on relationships between members of the first sampled social network users and the second social network users arising in the on-line social network; identifying, by the system, a cluster of social network users within the arrangement of the first sampled social network users and the second social network users of the social network graph; characterizing, by the system, the reduced sampling of the social network users based on the cluster of the social network users of the social network graph; and identifying, by the system, an outlier in the reduced sampling of the social network users based on the characterizing of the social network users, and based on collateral information combined with an intra-graph property of the social network graph, wherein the outlier does not conform to the social network graph.