Social networking sites are a part of everyday life for over a billion people worldwide. They show no sign of declining popularity, with social media use increasing at 3 times the rate of other Internet use. Despite this proliferation, mental healthcare has yet to embrace this unprecedented resource. We argue that social networking site data should become a high priority for psychiatry research and mental healthcare delivery. We illustrate our views using the world’s largest social networking site, Facebook, which currently has over 1 billion daily users (1 in 7 people worldwide). Facebook users can create personal profiles, socialize, express feelings, and share content, which Facebook stores as time-stamped digital records dating back to when the user first joined. Evidence suggests that 92% of adolescents go online daily and disclose considerably more about themselves online than offline. Thus, working with Facebook data could further our understanding of the onset and early years of mental illness, a crucial period of interpersonal development. Furthermore, a diminishing ‘digital divide’ has allowed for a broader sociodemographic to access Facebook, including homeless youth, young veterans, immigrants, patients with mental health problems, and seniors, enabling greater contact with traditionally harder-to-reach populations.