1. A method, comprising: reducing, by a system comprising a processing system including a processor, a sampling size of a 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 processing system, the population of the social network users to obtain first sampled social network users; sampling, by the processing system, the reduced population of the social network users utilizing a crawl algorithm to obtain second sampled social network users; generating, by the processing 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; characterizing, by the processing system, a cluster of social network users within the reduced sampling of the social network users; and identifying, by the processing system, an outlier in the reduced sampling of the social network users based on the characterizing of the cluster of social network users, wherein the outlier does not conform to the social network graph.