Technology-enhanced peer feedback (TEPF) activity has been increasingly investigated in L2 writing education. Researchers have conducted many review and meta-analysis studies on related research and identified factors influencing the activity effectiveness. However, few reviews have been conducted based on the activity theory that may clarify details of this learning approach and reveal how various factors influence the activity effectiveness. To fill in the gap, we reviewed 40 relevant articles from 2001 to 2021, following the activity theory. The findings showed that most TEPF activities were based on network-based social computing to enhance academic performance in English as L2 writing. College and university students with training experiences attended the activities independently or collaboratively as feedback givers and/or takers in anonymous, out-of-class, online settings for a long term. Learners may influence TEPF activities via peer feedback quality and the efficiency of peer interaction. Technology may influence the activities via peer feedback quality, learner emotions, and the efficiency of peer interaction and feedback generation, giving, taking and comprehension. Peer interaction may influence the activities via error identification, affective aspects, and knowledge and ideas of writing. Conditions may influence the activities via learners' experiences, trust in peers, devotion of effort and time, emotions and efficiency in peer interaction and feedback giving and taking. Mechanisms may influence the activities via learners' cognitive processes and active learning. Based on the results, we analysed the interactions in TEPF activities that may influence the activity effectiveness.