More than half of young people who died by suicide had previously self-harmed, a report looking at dozens of deaths found.
Bereavement, physical illness, school pressures and bullying were among the themes noted by researchers of a major new report into suicide in people aged under 20.
More than a quarter of the 130 children and young people in England whose deaths were considered in the report had expressed suicidal ideas in the week before they died, academics based at the University of Manchester found.
Between January 2014 and April last year, 145 young people died by suicide and researchers for the university's National Confidential Inquiry into Suicide and Homicide by People with Mental Illness (NCISH) looked at information in relation to 130 of those cases.
The majority, 70%, of those who died were male and suicide rates were found to rise sharply in older teenagers.
Sixty-six of those who died were aged between 10 and 17 – five of them were younger than 14.
Those behind the report said a death by suicide was often not down to one single cause, and could come after a build-up of different stresses.
Professor Louis Appleby, director of the inquiry, said: "There are often family problems such as drug misuse or domestic violence and more recent stresses such as bullying or bereavement, leading to a 'final straw' factor such as an exam or relationship breakdown."
The internet was a feature in some cases, researchers said, noting that there were instances of people expressing suicidal thoughts on social media and some people had been victims of online bullying.
Improving self-harm services and access to Child and Adolescent Mental Health Services was "crucial" to addressing the issue of suicide in young people, the report's authors said.
Professor Nav Kapur, NCISH head of suicide research, said: "Self-harm is strongly associated with increased future risk of suicide and is one of the main warning signs.
"It is crucial that there is improved help for self-harm and access to mental health care.
"However, with the variety of factors we found with this study, it is clear that schools, primary care, social services and youth justice all have a role to play."
The report, the first stage in a UK-wide analysis of suicides in people aged under 25, identified warning signs in some cases and highlighted the need for the provision of proper support, the Samaritans said.
The charity's head of external affairs Jacqui Morrissey said: "From the report, Samaritans is concerned that in the majority of cases there were clear warning signs that the young person was struggling to cope."
She added: "The message is clear, we need to make sure that the right support is in place for all young people, that all parents, carers and teachers understand about suicide risk and that young people are equipped to look after their emotional well-being before life's pressures become overwhelming."
The report sends a strong message that mental health services for young people need to improve, Brian Dow from Rethink Mental Illness said.
He added: "If nothing else this report shows how our mental health services need to improve. A recent report from Centre Forum found that over a quarter of young people are being turned away from mental health services; that's a disastrous situation.
"We must redouble our efforts to support children and young people and ensure that they are getting the help they need."
The Royal College of Nursing said early intervention was key to tackling the issue.
Ian Hulatt, professional lead for mental health, said: "Nurses working in mental health, and those working with children can give vital support and identify those at risk, and it is heartbreaking that young people have not known where to go or struggled to get help.
"Early intervention is absolutely crucial, which is why there needs to be a far greater focus on young people's mental health throughout the school system, and a real recognition in the health service of the devastating impact when these needs are not met."