Social networks are virtual spaces currently connecting over 3.8 billion users worldwide. The number of users and the number of different social networks is constantly growing, which indicates that technology-mediated daily life has become an integral part of life in the 21st century. It is indubitable that there are many advantages to technological progress, but the question remains whether the use of social networks necessarily contributes to the wellbeing and quality of life of every individual. Over the last decade, a growing number of studies have attempted to clarify the connection between the use of social networks and mental health. In the context of social networks, the most-studied factor is the subjective assessment of time spent on social networks and the type of social network use in those periods (active/passive use). In the context of mental health, the anxiety and depression have been most extensively studied, while self-esteem, fear of missing out, social comparison, and loneliness have shown themselves to be mediators/moderators in the association between social networks and mental health. However, it is extremely important to place existing research in the context of the COVID-19 pandemic. This review article presents the main findings in this field with the clear conclusion that further longitudinal and experimental studies are required to clarify the causal direction of this relationship and the potential protective and risk factors, especially in the context of the alterations in the importance of social networks in maintaining social contacts during the pandemic.