Some young people are facing "unacceptable barriers" in getting mental health support, a charity has warned.
A survey of 2,700 young people in the UK who had struggled with mental health issues found that only 9% felt it was easy to get the support they needed.
The YoungMinds poll of children and young adults up to the age of 25 found that two-thirds (66%) felt it was "difficult" to get help.
Only 6% said they believe there is enough support for children and young people with mental health problems.
Among young people who had accessed child and adolescent mental health services (CAMHS), 44% said they had found it hard to get an initial referral and 60% said they had faced a long wait between referral and assessment.
YoungMinds said that some youngsters start to self harm or feel suicidal while waiting for support.
The charity also surveyed 1,600 parents of children who had looked for support. Two-fifths (42%) of these parents said that they had struggled getting help from school or college while 29% reported problems getting help from a GP, according to the YoungMinds report.
"These results reflect what we hear every day from young people and parents - that, despite the great progress being made by campaigns like Heads Together to get people talking about mental health, as well as extra government investment, there can still be unacceptable barriers to getting help," said Sarah Brennan, chief executive of YoungMinds.
"Every day we get calls to our Parents Helpline from parents whose children can't get help at school, who've been waiting months for an assessment, or who have been told that they don't meet the threshold for treatment.
"We hear from young people who have started to self-harm or become suicidal while waiting for support.
"All the evidence shows that getting the right help quickly can prevent problems from escalating, so it's not good enough that around half of those young people who reach out for help are turned away."
Commenting on the figures, Bernadka Dubicka, chairwoman of the Royal College of Psychiatrists' child and adolescent faculty, said: "Children and parents are struggling to know when and where to seek help, and often finding themselves on long waiting lists for treatment once they do.
"This is almost entirely a symptom of under resourcing. With the number of child and adolescent psychiatrists down 6.6% since 2013, the waiting lists for treatment are only getting longer.
"If we do not have a robust mental health workforce, we will not be able to support the children in need of treatment."
An NHS England spokesman said: "Our five-year plan for improving mental health care is already beginning to make progress in much of the country, but decades of under-investment have left significant unmet demand, so while funding is up by £100 million and more children are getting timely help, it is clear that the sea-change in care we all want to see will take time to deliver."