This paper is about an investigation into student perceptions of peer affective factors during a Facebook-based collaborative writing activity among Turkish high school EFL learners. Two groups of three students, 16-year-old EFL learners at A2 level English proficiency (CEFR), undertook an online collaborative English short story writing exercise over seven weeks using Facebook. I gathered data from focus group discussions, online one-to-one chats and online discussion threads from both groups. Although small-scale, valuable insights were obtained into peer affective factors that emerged throughout the writing exercise, and were concerned with receiving/giving praise and motivational phrases, the use of informal language and humour in writing during the exercise as well as in relation to feeling comfortable with each other. The students claimed these factors greatly aided the development of their writing skills.