This study aimed to develop and implement an intervention, delivered via a website and Web app, to increase the uptake of sexual health services by young people. The intervention was co-designed with a group of 10 young people. Intervention mapping was used to guide development. To identify barriers and facilitators of access to sexual health services, three focus groups with 24 young people aged 13 to 19 years, and interviews with 12 professionals recruited from across a range of health and social services, were conducted. Data were analyzed using content analysis. Evidence was supplemented through a literature review. Barriers and facilitators were categorized as theoretical determinants and then suitable behavior change techniques (BCTs) for targeting them were selected. Targeted determinants were attitude, subjective norm, perceived behavioral control, and knowledge. Selected BCTs included “information about others’ approval,” “framing/reframing,” and “credible source.” The website/app enable users to search for services, access key information about them, watch videos about what to expect, and have key concerns removed/addressed. This is the first known digital evidence-based intervention to target this behavior described in the literature. A clear and full description of intervention development and content, including of theorized causal pathways, is provided to aid interpretation of future outcome evaluations.