The United Nations' agency for children says Aids is now the leading cause of death for African teenagers and the second most common killer for adolescents across the globe.
At a conference in South Africa on Friday, UNICEF said despite gains made among adults and babies with HIV, the number of 10-to-19-year-olds dying from AIDS-related diseases has tripled since 2000.
"Among HIV-affected populations, adolescents are the only group for which the mortality figures are not decreasing," the report says.
"Most adolescents who die of AIDS-related illnesses acquired HIV when they were infants, 10 to 15 years ago, when fewer pregnant women and mothers living with HIV received antiretroviral medicines to prevent HIV transmission from mother to child."
Many of them survived into their teenage years without knowing their HIV status.
However, among teenagers aged 15-19, 26 new infections occur every hour, and about half of the two million living with HIV in this group are in just six countries: South Africa, Nigeria, Kenya, India, Mozambique and Tanzania.
"In sub-Saharan Africa, the region with the highest prevalence, girls are vastly more affected, accounting for seven in 10 new infections among 15-19 year olds," the statement said.
The chief of UNICEF's HIV and AIDS division, Craig McClure, said children born with the virus were dying in their teens because there was not enough treatment aimed at adolescents.
Mani Djelassem, a 17-year-old activist who was born HIV-positive, said it was essential to educate teenagers about the disease and the medication that has been vital to saving her own life.