In this paper, considering the importance of opinion leadership and use of social networks for marketing, over 90 articles are studied and a comprehensive review of different studies in this area has been done. Studies show that different titles such as opinion leader, influential people, market maven and key player are used to refer to influential groups in social networks. Notwithstanding the similarity of these titles, in concept and identifying factors, a comprehensive classification for introducing such people’s properties is not done before. Hence, in this paper considering all the properties presented for the opinion leaders, influential people, market mavens and key players, three general categories including structural, relational and personal characteristics are presented. Furthermore, considering that in the literature, many methods have been introduced for the identification and selection of opinion leaders in social networks, in this article based on the studied opinion leader identification methods, appropriate parameters, including the input, identification and selection, and output are extracted in a comprehensive chart to accurately assess these methods. Comprehensive study, classifications and analysis of these studies are the main achievements of this article.