This article investigates the communicative styles of three different peer mentors in the context of online language learning, and considers their effect on student engagement. A key objective is to show how an innovative corpus-based technique, keyword analysis, can be used as a first step towards identifying communicative styles. We view communicative style as a linguistic means by which rapport is managed amongst participants (Spencer-Oatey 2008). Our primary data include 685 forum posts, of which 273 (over 26,000 words) were by the mentors at the heart of our study. We show that the three mentors have different communicative styles: different rapport management orientations are achieved in different ways. Furthermore, we bring together multiple data sources, including participants' posts and self-reported perception data. This allows us to find evidence on if and how communicative styles impact on student engagement and perception. We discovered that rapport enhancement aligns with increased active participation, especially if a self-effacement strategy is used, and positive student perception, but that the lack of such rapport does not automatically imply negative student perception.