With nearly 3.5 billion people now using some form of social media, understanding its relationship with personality has become a crucial focus of psychological research. As such, research linking personality traits to social media behaviour has proliferated in recent years, resulting in a disparate set of literature that is rarely synthesised. To address this, we performed a systematic search that identified 182 studies relating extraversion to social media behaviour. Our findings highlight that extraversion and social media are studied across six areas:1) content creation, 2) content reaction, 3) user profile characteristics, 4) patterns of use, 5) perceptions of social media, and 6) aggression, trolling, and excessive use. We compare these findings to offline behaviour and identify parallels such as extraverts' desire for social attention and their tendency to display positivity. Extraverts are also likely to use social media, spend more time using one or more social media platforms, and regularly create content. We discuss how this evidence will support the future development and design of social media platforms, and its application across a variety of disciplines such as marketing and human-computer interaction.