BACKGROUND: Young people regularly use online services to seek help and look for information about mental health problems. Yet little is known about the effects that online services have on mental health and whether these services facilitate help-seeking in young people. OBJECTIVE: This systematic review investigates the effectiveness of online services in facilitating mental health help-seeking in young people. METHODS: Using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, literature searches were conducted in PubMed, PsycINFO, and the Cochrane library. Out of 608 publications identified, 18 studies fulfilled the inclusion criteria of investigating online mental health services and help-seeking in young people aged 14-25 years. RESULTS: Two qualitative, 12 cross-sectional, one quasi-experimental, and three randomized controlled trials (RCTs) were reviewed. There was no change in help-seeking behavior found in the RCTs, while the quasi-experimental study found a slight but significant increase in help-seeking. The cross-sectional studies reported that online services facilitated seeking help from a professional source for an average of 35% of users. The majority of the studies included small sample sizes and a high proportion of young women. Help-seeking was often a secondary outcome, with only 22% (4/18) of studies using adequate measures of help-seeking. The majority of studies identified in this review were of low quality and likely to be biased. Across all studies, young people regularly used and were generally satisfied with online mental health resources. Facilitators and barriers to help-seeking were also identified. CONCLUSIONS: Few studies examine the effects of online services on mental health help-seeking. Further research is needed to determine whether online mental health services effectively facilitate help-seeking for young people.