Three out of four parents say their children's mental health deteriorated while waiting for NHS support, according to a report by charity YoungMinds.
It says a fresh approach to supporting young people was needed, including more help from local community groups.
Without it, young people could start to self-harm, become suicidal or drop out of school, it said.
Laura, 19, ended up overdosing after repeated delays in accessing help.
She first experienced depression at the age of 11 and her problems reappeared in the run-up to her GCSEs, made worse when two appointments had to be postponed as they clashed with exams.
"I just had to wait it out, I kept getting worse, I got really suicidal.
"I was missing lots of sixth form and not talking to anyone," Laura says.
'Somebody to talk to'
She lost faith in mental health services completely when a letter said her referral to a specialist had been cancelled because of missed appointments.
A two-year stay in psychiatric hospital followed, most of it in an intensive unit where she was eventually diagnosed with borderline personality disorder.
Laura says she felt like a burden, felt like people didn't care - "and this was reinforced by the services that were supposed to help".
She says some temporary support would have made all the difference.
"Just somebody to talk to, to manage the suicidal thoughts. If there had been a youth group to go to, somewhere..," Laura says.
The YoungMinds report said there was "a black hole in youth and community services" where essential early support could be provided.
It said hundreds of youth centres had closed and thousands of youth workers had been lost, which meant young people had fewer trusted adults to help them cope.
The charity is calling for extra investment in youth clubs, churches, cafes or hostels to provide this local support.
The charity's survey of more than 2,000 parents and carers whose children have looked for mental health support, found that:
- 76% said their children had become more unwell before they could access treatment
- 86% of parents whose children had waited more than six months said their offspring's health had deteriorated, including 64% who said their children's mental health had deteriorated a lot
- 69% said neither they nor their children had been told of any other form of support while they were waiting for children and adolescent mental health services (CAMHS)
The charity said the government's recent plans to introduce mental health support teams in schools were a step in the right direction, but would cover "less than a quarter of areas by 2022-23".
NHS England said funding was rising for mental health services for the young, and further priorities would be set out in a long-term plan for the NHS this autumn.
A spokesperson said: "The NHS is only halfway through an ambitious programme of transformation where access to mental health services will significantly expand by 2021 and an additional 70,000 children and young people will get help."
NHS England said the government, schools and councils would all need to work together to meet the needs of children and young people.
Emma Thomas, chief executive of YoungMinds said: "The crisis in young people's mental health is real and it's urgent.
"Crucially we also need to invest in new ways for young people to get help early on, before they require more specialist treatment.
"Every community must have spaces where young people can go to feel safe, work through how they're feeling, and learn strategies to help them manage and start to feel better."
Laura is now back at college studying for her A levels, and she has a key worker who checks up on her regularly. Her life has turned around.
Cllr Ian Hudspeth, chairman of the Local Government Association's Community Wellbeing Board, said he wanted to see councils and schools given the funding to offer independent mental health counselling so that pupils have access to support as and when they need it.
"We need to develop a system that says "yes" to all children and young people, rather than "no" when they ask for help.
"Children and their families need help and support right now - depression, anxiety, bereavement and family crises do not wait."
He added: "The government also needs to work with the LGA and councils to make sure this is a local area-led approach, rather than just NHS."