YouGov poll also reveals two in five suffered suicidal thoughts, self-loathing or panic attacks as result of unemployment

Hundreds of thousands of young people feel they have nothing to live for, with the long-term unemployed being particularly pessimistic about their prospects, a youth charity has warned.

The warning is based on the findings of a YouGov poll for the Prince's Trust Macquarie Youth Index, which also reports that 40% of jobless young people have experienced symptoms of mental illness, such as suicidal thoughts, or feelings of self-loathing and panic attacks, due to their unemployment.

Of those polled, 9% said they did not "have anything to live for". This statistic, if applied to the population as a whole, equates to 750,000 people aged between 16 and 25, the Prince's Trust said.

The situation was found to be worse among the long-term unemployed (those unemployed for six months or more), with 21% agreeing.

Paul Brown, Prince's Trust director, said: "We need to recognise that unemployment doesn't just lead to economic disadvantage for young people but can scar them.

"There are a very large number of people still unemployed, lacking all hope for the future. We have a duty to make sure there's something to look forward to."

There are more than 900,000 unemployed people aged 16 to 24 in Britain. The Prince's Trust claims that more than 440,000 of them face long-term unemployment.

Brown said the government, private sector and charities had a responsibility to work together to ensure the young and vulnerable were not left behind as the economy recovered.

The Prince's Trust said it will support 58,000 disadvantaged young people this year. But Brown added that they could help many more with greater funding. Three in four young people supported by the charity moved into work, education or training, the trust said.

Brown said the vulnerable had suffered most as graduates lowered their career ambitions, taking jobs previously filled by people with fewer qualifications. "Those at the bottom of the pile are really struggling," he added.

The report, using online interviews in October and November with 2,161 people aged 16 to 25, found other experiences directly attributed by young people to unemployment included self-harm, and using large quantities of alcohol and drugs.

One in three of the long-term unemployed said they had contemplated suicide; one in four said they had self harmed. They were also more than twice as likely to be prescribed antidepressants compared with their peers (25% compared with 11%).

Shirley Cramer, chief executive of the Royal Society for Public Health, said of the research: "[It] proves that unemployment is a public health issue. It is one that must be tackled urgently and it is essential that youth unemployment is added to the public health agenda."

The survey also found three-quarters of unemployed young people said they would not ask for help if they were struggling to cope, compared with 56% of all young people.

Danielle Stevens, 21, from Hackney in London, a job ambassador for the Prince's Trust, used her own experiences of unemployment when she was a teenager to help other young people get their lives back on track. "When I was unemployed, my confidence went down and I suffered from depression. Unemployment, especially for a young person, can make them feel very down. I say to them, I was one of them but with hard work and support you can make it."

Of those polled, 281 were not in employment, education or training and 166 had been unemployed for six months or more.

• The headline of this article was updated on 2 January 2014. The original headline stated: One in 10 young British jobless 'have nothing to live for'.