Background and Objective: The COVID-19 pandemic has increased psychological distress and the use of social media, especially in young people. The continual use of social media can undermine people’s mental well-being. However, social media can provide peer support by enabling people to share their mental health experiences. Still, little is known about mental health communication on social media during the pandemic. The aim of this review is to describe the existing research related to mental health communication on social media during the COVID-19 pandemic. Methods: The peer-reviewed literature was reviewed using the search terms, such as social media, mental health, and COVID-19. The databases used were APA PsycINFO, CINAHL, Pubmed, and Web of Science. A manual search was also conducted. Studies were excluded if the study population consisted of the elderly or social-/healthcare professionals, or if the mental health conversations were related to specific health problems or specific peer-support groups and networks. The search resulted in 1970 references, of which 19 studies were selected. Results: The studies (N=19) were conducted in North America (63%), in Asia (32%), and in Australia (5%). Machine learning was used in the majority of the studies. The studies examined communication on Twitter (58%), Reddit (26%), Sina Weibo (11%), and YouTube (5%). The communicated mental health topics included depression, suicidal thoughts, anxiety, fatigue, poor sleep quality, stress, and feelings of loneliness and fear. Peer support and advice were also communicated. Conclusions: Mental health topics are communicated via social media, suggesting that social media platforms are a useful method to identify ongoing prevalent, and even potentially emerging, mental health topics. The existing research focuses mainly on Twitter; therefore, research is needed on other commonly used social media platforms among adolescents, such as YouTube. Research regarding users’ experiences with peer support on social media is also needed.