This paper reports on a task-based language teaching course in Second Life. The data set consists of transcribed recordings and a teacher interview. Focusing on how the teacher facilitated student participation, this paper aims to explore the discourse functions in the teacher language output and then to address the teacher roles in three different task phases. All the turns produced by the teacher and the students were counted, the teacher language output in the recordings was classified into 19 discourse function categories, and then all the discourse functions were classified into six teacher roles. The results show that the during-task phase was student output oriented. This study reveals that in the pre-task phase the teacher used the largest number of types and tokens of discourse functions, and played a significant technical and social role. In the during-task phase, the teacher focused on motivating students to participate, monitoring student activities, and providing task support. In the post-task phase, the teacher was a language guide. While the teacher roles that were most prominent varied in the three task phases, the teacher was found to play four roles consistently in the three task phases: monitor role, motivator role, language guide role, and social role.