We examined online and offline social supports for sexual minority adolescents, underscoring the understudied developmental period of early adolescence and the mental outcome of loneliness. Stemming from a larger study in the northeast U.S., 967 youth participants were 26% sexual minority, 53% female, 45% male, and 2% other/nonbinary (mean age = 13.1, SD = 1.52). LGBTQ+ youth reported significantly higher levels of loneliness compared to their heterosexual counterparts. To understand potential sources of social support while exploring their sexual identities, we compared the experiences of LGBTQ+ youth at both ends of the loneliness spectrum. Gaining knowledge about their sexual orientation from LGBTQ+ organization websites, participating in gender–sexuality alliances, and using TikTok or Instagram were associated with lower levels of loneliness. Providing social support to online friends was associated with lower loneliness; however, receiving online support was not associated with lower loneliness. Furthermore, proactive social media engagement such as posting uplifting content, joining online communities, or raising awareness about social issues were associated with lower levels of loneliness. The results provide guidance on specific youth behaviors and online communities beyond a focus on screen time while highlighting the continued need for social support to ameliorate loneliness, such as gender–sexuality alliance networks.