Young people can be reluctant to seek help for a mental health problem due to many factors, and research suggests that early and meaningful intervention within this demographic is essential to support improved quality of life and reduce youth death by suicide. The role of informal sources of help in youth mental health help-seeking pathways is an important subject however, there are no reviews on this topic. The aim of this scoping review was to map the existing literature regarding how informal sources of help affect young people’s access to, engagement with and maintenance in professional mental health care. Nine databases were searched for original peer-reviewed research published between 1994 and 2021 with young people aged 10–25 years. A thematic analysis was performed on 32 studies that met selection criteria. Two key themes were identified: 1. Informal helpers as supportive intermediaries and 2. Informal helpers as obstructive forces. This review found that informal sources of help are dynamic and essential pathway agents in helping or hindering young people with accessing and staying engaged in professional mental health care. Further research on this topic with young people about their actual help-seeking experiences is required. Through an improved understanding of how these interpersonal relationships function within a young person’s help-seeking process, on a spectrum of supportive to obstructive behaviour, services and practitioners can ensure the provision of responsive and appropriate support to young people and their families, facilitating service use and ensuring better outcomes for young people’s mental health and quality of life.