Nearly a quarter of 16-year-old girls in England have been in contact with NHS mental health, autism and learning disability services in the past year.
New figures show a large rise in the number of children and teenagers seeking help, with almost a million contacting the NHS.
There has been a rise across all age groups, with almost a fifth more people needing support compared with three years ago.
Data shows a 29% rise in 2021/22 in the number of under-18s in contact with mental health, learning disability and autism services when compared with 2020/21.
Some 992,647 needed support in 2021/22 - up from 768,083 in 2020/21 and 763,888 in 2019/20.
Overall, 18% of the country's 16-year-olds (114,203) and 17% of 17-year-olds (101,694) have been in contact with those services over the past year.
Girls aged 16 were most likely to need support with 23% (69,580) seeking help in the past year.
The number of 11 to 15-year-olds in contact with the services also increased, from 359,681 in 2020/21 to 498,558 to 2021/22 - a 39% rise.
Olly Parker, head of external affairs at YoungMinds, said: "These figures demonstrate the unprecedented crisis happening in young people's mental health, with almost one in five 16-year-olds across the country in contact with mental health services. The situation is unsustainable.
"Thousands of young people are seeking mental health support but too many are being told to wait, struggling to cope and hitting crisis point before they get help.
"We know young women in particular face a wide range of pressures that may affect their mental health - from school stress to difficult relationships with family or friends and problems and concerns about body image often exacerbated by social media.
"For years politicians have promised to end the crisis in young people's mental health. But the reality is that with every month of inaction, things are getting worse."
The NHS Digital data shows that 3,256,695 people of all ages were in contact with mental health, learning disabilities and autism services at some point in the year - 992,647 of these were under 18.
The overall total has risen by almost a fifth in three years, up from 2,803,244 in 2020/21, 2,878,636 in 2019/20 and 2,726,721 in 2018/19.
This means 5.8% of the population of England have been in contact with NHS mental health services in the past year.
Anyone feeling emotionally distressed or suicidal can call Samaritans for help on 116 123 or email email@example.com in the UK. In the US, call the Samaritans branch in your area or 1 (800) 273-TALK.