Background Despite widespread use, little is known about how adolescents and young adults (AYA) with cancer use social media (SM). This research characterized use and self‐reported SM experiences among AYA with cancer. Procedure AYA, aged 12‐26 years, receiving cancer care completed a mixed‐methods survey regarding SM experiences. Clinical information was obtained from the electronic medical record. Data were analyzed with descriptive statistics, t tests, and qualitative content analysis. Results Thirty‐nine AYA with average age 16 (SD = 3.2) years participated. Most were Caucasian (92%) males (54%). Participants had leukemia/lymphoma (56%), solid tumors (33%), and brain tumors (10%). Nearly all (97%) used SM, with YouTube, Snapchat, and Instagram being the most popular. AYA self‐reported lower SM use than their smartphone data indicated (2.8 hours/day, SD = 1.2 vs 3.4 hours/day, SD = 1.3; P < 0.001). Participants used SM to obtain information about their cancer (45%), post about cancer (47%), and read about others’ cancer experience (50%). One‐third made a friend with cancer through SM (32%). Qualitative results indicated that AYA had positive cancer‐related SM experiences, including feelings of support (54%), community (27%), distraction (8%), and inspiration (8%). Most denied negative experiences (78%); however, 17% reported cyberbullying related to cancer. Conclusions AYA with cancer avidly use SM, noting it provides a sense of support and community. However, one‐sixth reported cancer‐related cyberbullying. AYA oncology providers have an opportunity to enhance positive and blunt negative SM interactions by addressing and guiding SM use in AYA patients.