Social media platforms such as WhatsApp are increasingly used in formal education settings. However, there is little research to guide educators on how to set up effective peer tutoring groups on social media platforms, particularly between tutors and tutees who rarely meet face-to-face. In the context of a WhatsApp mathematics tutoring project, we present evidence-based principles to guide the establishment and operation of peer tutoring groups on a social media platform. The development of the principles followed a design-based research framework, based on theories about peer learning, participation barriers to social media use in a low socio-economic setting, and input from participants, who were high school students and university students in Cape Town, South Africa. The refined principles provide guidance for others in similar settings who aim to use tutoring groups on a social media platform to achieve education goals.