The increasingly influential development and internet has caught a wealth of scholarly attentions, shedding light on various aspects of the field, for instance, web applications, and their sociability and usability. However, hardly any study is thoroughly applicable to Macao where virtual communities can intercourse intensively with traditional communities with its characteristics of limited geographical area, highly dense population, and diffusive community culture. This paper, based on Maslow's Hierarchy of Needs (1943), common interest introduced by Ridings and Gefen (2004), and theories of common bond and common identity (Prentice et al., 1994), proposes a conceptual framework to understand why netizens engage in a special interest online forum and what qualifications the forum has to be sustainable. Findings suggest that the virtual community providing different levels of needs satisfaction, such as common interest, love, esteem, and self-actualization, and building bonds between users could attract and sustain members' engagement. During the study, growth or change of needs were also frequently observed. Many interviewees indicated that they joined for information access or friendships at first, later on they sought to have esteem needs, once they achieved the lower level needs, they sought to have the higher- esteem needs, or self-actualization needs. These phenomena also echoed with Maslow's (1943) Hierarchy of Needs.