Young people are most at risk of sexually transmitted infections
Too many young people are unaware of the risks of HIV, Unicef has warned.
Those aged 16 to 24 account for 10% of all new diagnoses in the UK and young men who have sex with men are most at risk, a report said.
More strategies to encourage young people to practise safe sex and have better access to sexual health clinics are needed, it concluded.
The UK has the highest number of new HIV infections in Western Europe - more than 7,700 in 2007.
People who move to the UK from sub-Saharan Africa are also particularly at risk.
Globally, girls and young women remain far more vulnerable to HIV infection than young men, accounting for two-thirds of the 5.5 million 15 to 24-year-olds with HIV worldwide.
The report, which looked at problems faced in all areas of the world, said the majority of young people still lack comprehensive and correct information on HIV infection, or do not have the power to act on that knowledge.
Anita Tiessen, deputy executive director of Unicef, UK said many young people had heard of HIV and Aids but they did not know how it spread or whether they were at risk.
"More attention has to be given to preventing the spread of HIV by working alongside young people to make sure that prevention work is designed and delivered in a way that is 'youth friendly' and really meets their needs.
"HIV can be best avoided through a three-pronged approach - by making sure people have the right information, can access health services, and get protection when they need it," she added.
The Unicef report also pointed to recent research which shows that some young people in the UK, especially young women, find it hard to access sexual health services experiencing difficulties in making appointments and long waiting times.
Sexual health services designed to address the needs of young people are urgently needed, it concluded.
Lisa Power, head of policy at the Terrence Higgins Trust, said young people knew less about HIV now than they used to and a lack of sex and relationships education in schools was partly to blame, although there are now plans to add it into the curriculum.
"We need to up the level of public information on HIV and it's partly about encouraging safe sex and partly about decreasing stigma of HIV.
"By next year there will be 100,000 people living with HIV in the UK and one in four of those are undiagnosed and we need to support those who are undiagnosed to get tested."
She added the UK had made great advances in the treatment of HIV but that had contributed to making it "invisible".
A Department of Health spokesperson said HIV prevention remained a priority.
"That is why we continue to provide funding for the Terrence Higgins Trust and for the African HIV Policy Network for work with the groups most at risk of HIV in the UK - gay men, and African communities.
"This is additional to our Condom Essential Wear campaign and joint awareness campaigns with the Department for Children, Schools and Families for young people which target other sexually transmitted infections."