The majority of teens experience challenges with stress and depression in the United States. However, they lack the resources to access traditional face-to-face mental health care and participate in Human Computer Interaction research. Researchers have successfully used Asynchronous Remote Communities (ARC) to study marginalized and geographically distributed adult participants by enrolling them in private online groups and conducting structured activities to understand their needs. To increase access and develop empirical understanding of teenagers' mental health needs, I led three studies that enrolled a total of 40 teens and 13 clinicians in ARCs to conduct 20-minute weekly activities in anonymous private online groups on Slack for ten weeks. In the first study, collaborators and I elicited current strategies, tools, and unmet needs of teenagers (n=23) for stress management. We found that coping strategies of teens were individual and based on their perception of control over stressors. Teens also wanted support from technologies to support reflection, understand their mood, and navigate boundaries in sharing about mental health with adults and peers. In the second study, we used ARC for ten weeks to understand needs and obtain feedback from clinicians (n=10) and teens (n=8) on adapting the evidence-based practice of behavioral activation (BA) for depression management delivered through online platforms such as Slack. We designed low-fidelity prototypes of BA interventions to support teens in understanding the relationship between mood and activity and learning to practice goal-directed behaviors to improve mood. Based on our analysis, both teens and clinician participants wanted support asynchronous support as a supplement to in-person therapy and most teens preferred to preserve and enhance online peer support. Teens and clinicians also raised concerns about safety, privacy, and moderating the online group which need to be balanced with the potential benefits of learning coping strategies, increased access, and asynchronous human connection. Informed by BA, teens' design needs, and clinicians' expertise, we adapted the ARC method in the third study to develop a high-fidelity prototype and evaluate the feasibility of a guided ARC intervention. We designed and developed an app called ActivaTeen on Slack which functioned as an interactive smart diary application that supported BA modules on activity logging, reflecting on upward and downward spiral of mood, and SMART goal planning. We enrolled nine teens and three clinicians on Slack to understand the feasibility of using the guided ARC intervention for eight weeks followed by interviews. We found that engagement varied at an individual level for teens with depression and designers need to account for avoidance, support reflection with possibilities of missing data, and navigate the burden of asynchronous clinical work in using guided ARC. Through my dissertation research, I aimed to understand how the design of remote technology can support teenagers to cope with stress and depression and empower their choice to act on healthy coping behaviors. The main contributions of my work include (1) an empirical understanding of needs to design for teen stress and depression management, (2) design and development of a guided ARC intervention using BA, (3) reflection on lessons learned using the ARC method for engaging with teens and clinicians, and (4) design considerations for using the process of human centered design for teen mental health. This work is a step towards identifying opportunities and challenges in using guided ARC to integrate evidence-based practices in designing for mental health and supplement face-to-face or synchronous online therapy.