This research merges advice from experts, literature review and statistical studies to figure out the main concerns, factors and variables of users when choosing social network sites. Analysis in relation to hierarchy and Analytic Hierarchy Process (AHP) to acquire the weight of each variable was also conducted in this research. The major findings of this study about top 5 critical success factors for Facebook are listed in follow: System stability, Smooth network connection, Easy to build relationship, The confidentiality of private information and Friend's recommendation. The results provide the user for the reference to manage relationship and social network sites.