Mobile phone usage is increasingly prevalent among urban teenagers in Lagos, Nigeria, for various purposes including entertainment and communication. However, its role in mental health support has received limited attention. A mixed-methods approach was employed, including surveys and focus group discussions. Data were analysed using descriptive statistics and thematic analysis. The survey revealed that approximately 75% of respondents used mobile phones for mental health support, primarily to connect with peers who shared similar experiences (theme). Mobile phone usage in mental health support has been well-received by urban teenagers in Lagos. Community engagement was effective when facilitated through peer-led initiatives. Further research should focus on the long-term impact of mobile phone-based interventions and explore integration with other community resources. Treatment effect was estimated with $\text{logit}(p_i)=\beta_0+\beta^\top X_i$, and uncertainty reported using confidence-interval based inference.