A young person is infected with HIV every 14 seconds, a report from the United Nations Population Fund reveals.
Some 6,000 young people are infected every day.
Around 6,000 people between the ages of 15 and 24 catch the disease every day.
Half of all new infections are now in people under the age of 25 and most of these are young women living in the developing world.
Thoraya Ahmed Obaid, executive director of the fund, said urgent action was needed to tackle what she described as a "global catastrophe".
The report, called The State of World Population, shows that nearly half of the world's population is under the age of 25. Of these, 87% live in developing countries.
One in four or 238 million live in extreme poverty, surviving on less than $1 a day.
Some 57 million young men and 96 million young women between the ages of 15 and 24 cannot read or write.
More than 13 million children under the age of 15 have lost one or both parents to Aids.
The report suggests that poverty, illiteracy and poor services are combining to help spread HIV among young people.
"Aids has become a disease of young people, fuelled by poverty, gender inequality and a severe lack of information and services," said Ms Obaid.
"They lack basic information on reproductive health and how to protect themselves from early pregnancy, HIV/Aids and other sexually transmitted infections."
'Women at risk'
The report shows that two out of three young people with HIV are female.
In sub-Saharan Africa, women account for 67% of young people who are HIV positive. In Asia, the figure is 62%.
The report says that many women in developing countries are unable to protect themselves against the disease.
In many cases, they do not know how it is spread. In Somalia, for instance, only 26% of females have heard of Aids and only 1% know how to protect themselves.
Others simply do not have the power to negotiate safer sex or refuse sex.
Millions of young girls marry older men every year. In many cases, the men are much more sexually experienced and girls find they are unable to get them to use a condom.
Recent research in Kenya and Zambia has found married girls are more likely to be HIV positive than their unmarried counterparts.
The report calls for better health education programmes and improved services to help get safe sex messages across to young people.
"There is clear evidence from Africa, Asia and Latin America that well-designed information and education programmes do lead to safer, healthier behaviour," said Ms Obaid.
"Far greater support is needed for sexuality education and HIV prevention programmes for young people both in and out of school."
She said the report should make stark reading for everyone.
"This report is a wake-up call," said Ms Obaid. "It is a wake-up call to listen to young people and acknowledge their needs.
"It is a wake-up call to increase funding and expand information and services to young people. It is a wake-up call to support them so that they can lead healthy, productive and dignified lives," she said.
"The world can no longer afford to take half measures as Aids wipes out growing numbers of the new generation.
"This is not just a public health issue. This is a global catastrophe that demands urgent global action."