Knowledge has become a key factor to success in social environments and virtual communities. Also, human resources are a critical part of the creation and dissemination of the knowledge-based resources in virtual communities. Comprehensive understanding of virtual community dynamics can aid us to address critical organizational and information systems issues. Furthermore, virtual communities have gained high acceptance for people to learn and share knowledge. However, the detailed review and deep discussion in this filed are very rare. Therefore, this paper reviews and discusses the recently introduced mechanisms in this field as well as providing a deep analysis of their applied domains. This survey will help to a conceptual understanding of nature and the position of KS in virtual communities. Moreover, the drawbacks and benefits of the reviewed mechanisms in three categories such as social factors, motivation factors, and medical factors have been discussed and the main challenges of these mechanisms are highlighted for developing more efficient KS in virtual communities in the future. The obtained results indicated that helps the creativity and the success of the organizations, saving time and cost, reducing medical errors and also optimizing the learning effect. Trust is also the greatest prerequisite for KS.