Young unemployed adults need more help to deal with mental health problems, the Prince's Trust charity has warned.
One in 10 youngsters questioned in a survey disagreed that "life was really worth living". Those not in work or education were less likely to be happy.
Polling company YouGov questioned 2,004 people aged 16-25 online in October.
Paul Brow, of the Prince's Trust, said the study showed there were thousands of young people who "desperately" needed support.
He added: "Often young people who feel they have reached rock bottom don't know where to turn for help."
Of those questioned, 29% said they are less happy now than they were as a child and one in five said they felt like crying "often" or "always".
Almost half (47%) said they were regularly stressed.
Young people tell us that family is key to their happiness, yet too often we find they don't have this crucial support
Martina Milburn, Prince's Trust
The feelings of negativity among those who took part in the survey were higher among those not in work, education or training.
Young people who had left school but did not have a job or a place on a training course were twice as likely to feel that their life had no purpose.
Key to levels of happiness, were relationships with family and friends, although health, money and work were also important.
The Prince's Trust says it plans to train all its frontline staff to recognise mental health problems in what it calls an increasingly vulnerable generation.
Chief executive Martina Milburn said: "Young people tell us that family is key to their happiness, yet too often we find they don't have this crucial support.
"At the Prince's Trust we help vulnerable young people, steering them away from false support systems such as drugs, alcohol and dangerous gangs and providing them with a sense of purpose again."
Ross Hendry, head of public policy at the Action for Children charity, said the report highlighted "serious issues" which needed to be addressed.
"Children must be given the chance to speak out, be heard and participate in setting the political agenda about issues affecting their lives, if we are to build stronger, safer and more inclusive communities," he said.
A spokesman for the Department for Children, Schools and Families said: "The government wants to make this the best country in the world to grow up and the Children's Plan sets out how we will do this with more support for families, world class schools, and exciting things for young people to do outside school, and more places for children to play.
"In a survey of 110,000 pupils last year 93% of children said that they felt happy about life.
"But we know childhood isn't good for every child and we will continue to focus on the problems that exist for some."
The Prince's Trust worked with YouGov to compile what it is calling a Youth Index based on the figures from the survey.
After ranking issues such as work, accommodation, family relations and health on a scale from one to seven the Youth Index is presented as a percentage to indicate young people's happiness (71) and confidence (74) - producing an overall average of 73 for their well-being.
This page is best viewed in an up-to-date web browser with style sheets (CSS) enabled. While you will be able to view the content of this page in your current browser, you will not be able to get the full visual experience. Please consider upgrading your browser software or enabling style sheets (CSS) if you are able to do so.