Early detection and intervention can counteract mental disorders and risk behaviours among adolescents. However, help-seeking rates are low. School-based screenings are a promising tool to detect adolescents at risk for mental problems and to improve help-seeking behaviour. We assessed associations between the intervention “Screening by Professionals” (ProfScreen) and the use of mental health services and at-risk state at 12 month follow-up compared to a control group. School students (aged 15 ± 0.9 years) from 11 European countries participating in the “Saving and Empowering Young Lives in Europe” (SEYLE) study completed a self-report questionnaire on mental health problems and risk behaviours. ProfScreen students considered “at-risk” for mental illness or risk behaviour based on the screening were invited for a clinical interview with a mental health professional and, if necessary, referred for subsequent treatment. At follow-up, students completed another self-report, additionally reporting on service use. Of the total sample (N = 4,172), 61.9% were considered at-risk. 40.7% of the ProfScreen at-risk participants invited for the clinical interview attended the interview, and 10.1% of subsequently referred ProfScreen participants engaged in professional treatment. There were no differences between the ProfScreen and control group regarding follow-up service use and at-risk state. Attending the ProfScreen interview was positively associated with follow-up service use (OR = 1.783, 95% CI = 1.038–3.064), but had no effect on follow-up at-risk state. Service use rates of professional care as well as of the ProfScreen intervention itself were low. Future school-based interventions targeting help-seeking need to address barriers to intervention adherence.Clinical Trials Registration: The trial is registered at the US National Institute of Health (NIH) clinical trial registry (NCT00906620, registered on 21 May, 2009), and the German Clinical Trials Register (DRKS00000214, registered on 27 October, 2009).