This study explores the promise and possibility of using Facebook as a new pedagogical tool to enhance college EFL learners` writing. Facebook is the most popular social networking site (Vaughan-Nichols, 2013) and its use in L2 learning is only beginning to emerge in the current literature (Jin, 2013). This study attempts to identify how Facebook use can be beneficial for EFL writing instruction. The research questions are 1) In what ways does using Facebook help to promote college EFL learners` development of writing? and 2) How do learners view the effectiveness of using Facebook for their writing instruction? This study employed a virtual ethnography approach and used qualitative interviews and a post-course survey as primary methods to collect data. The findings indicated that Facebook offered an effective online learning space for learners to actively engage in the course writing tasks. For example, it increased learners` motivation and confidence, decreased learners` anxiety of writing in English, and enabled various peer feedback and communicative writing. In addition, learners showed overall positive perceptions of using Facebook in their writing course. It suggests the positive possibility of using Facebook as a new pedagogical tool for EFL writing instruction.