Mental health problems among adolescents have become an increasing public health concern, particularly in the context of widespread social media use. Mental health literacy and help-seeking behaviors play a critical role in the early recognition and management of psychological difficulties. This study aimed to examine the influence of school and social factors, together with social media use, on mental health literacy and help-seeking behaviors among Thai adolescents. A cross-sectional survey was conducted among 128 secondary school students in Thailand (mean age = 16 years). Data were collected using a structured self-administered questionnaire assessing demographic characteristics, daily social media use, mental health literacy, help-seeking readiness, stigma-related attitudes, and perceptions of the school mental health consultation environment. Descriptive statistics, chi-square tests, and multiple linear regression analyses were performed. Overall, participants demonstrated moderate to high levels of mental health literacy (Mean = 3.99, SD = 0.83) and help-seeking readiness (Mean = 4.18, SD = 0.75), with generally positive attitudes toward stigma reduction. Although social media use was prevalent, daily duration of use was not significantly associated with mental health literacy. In contrast, a supportive school mental health consultation environment emerged as a statistically significant predictor of mental health literacy (β = 0.28, p = 0.002), while social media use showed no predictive effect.These findings suggest that adolescents’ mental health literacy and help-seeking behaviors are shaped more strongly by school-based contextual factors than by the amount of time spent on social media. Strengthening supportive school mental health environments may therefore be more effective than focusing solely on reducing social media use in promoting adolescent mental well-being.