Background: Many current challenges of evidence-based practice are related to ineffective social networks among health care professionals. Opportunities exist for multidisciplinary virtual communities to transcend professional and organizational boundaries and facilitate important knowledge transfer. Although health care professionals have been using the Internet to form virtual communities for many years, little is known regarding "why" they join, as most research has focused on the perspective of "posters," who form a minority of members. Objective: Our aim was to develop a comprehensive understanding of why health care professionals belong to a virtual community (VC). Methods: A qualitative approach will be used to explore why health care professionals belong to an intensive care practice-based VC, established since 2003. Three asynchronous online focus groups will be convened using a closed secure discussion forum. Participants will be recruited directly by sending emails to the VC and a Google form used to collect consent and participant demographics. Participants will be stratified by their online posting behaviors between September 1, 2012, and August 31, 2014: (1) more than 5 posts, (2) 1-5 posts, or (3) no posts. A question guide will be used to guide participant discussion. A moderation approach based on the principles of focus group method and e-moderation has been developed. The main source of data will be discussion threads, supported by a research diary and field notes. Data analysis will be undertaken using a thematic approach and framed by the Diffusion of Innovation theory. NVivo software will be used to support analyses. Results: At the time of writing, 29 participants agreed to participate (Focus Group 1: n=4; Focus Group 2: n=16; Focus Group 3: n=9) and data collection was complete. Conclusions: This study will contribute to a growing body of research on the use of social media in professional health care settings. Specifically, we hope results will demonstrate an enhancement of health care professionals' social networks and how VCs may improve knowledge distribution and patient care outcomes. Additionally, the study will contribute to research methods development in this area by detailing approaches to understand the effectiveness of online focus groups as a data collection method for qualitative research methods.