A child sexual exploitation report has found police made no sustained effort to find out who was responsible for abusing children in the care system.
The review into 22 abuse cases in Northern Ireland criticised the authorities for not doing enough.
The young people went missing a number of times over a 20-month period while being looked after in the care system.
The Police Service of Northern Ireland (PSNI) said it has recently made policy changes aimed at keeping children safe.
In September 2013, the PSNI said it had begun a major investigation into the sexual exploitation of children and young people who had gone missing from care in Northern Ireland.
Officers said they had identified 22 people, aged between 13 and 18, who may have been sexually exploited.
The PSNI investigation was known was Operation Owl.
Thursday’s report, examining the PSNI response, has been published by the Safeguarding Board for Northern Ireland.
It said PSNI officers were effective in locating the teenagers and returning them to the care system.
However, it found that they failed to properly examine the extent of the child sexual exploitation taking place and their attempts to find and stop the abusers was – in the words of the review – “limited and inconsistent”.
While there is praise for the help offered by some staff from residential care homes, Stormont’s Health Minister Simon Hamilton said that the report shows not enough support was given to protect the teenagers from harm or the risk of harm.
He said the review had identified “a significant gap” in knowledge about perpetrators of child sexual exploitation.
The head of the PSNI’s Public Protection Branch, Det Ch Supt George Clarke said that following Operation Owl, the PSNI has “implemented a number of changes in our approach to handling this issue to ensure we are doing everything we can to keep children and young people safe”.
“Indeed, in April of this year, the PSNI formed the Public Protection Branch which is now responsible for policy and practice in relation to a number of areas including child sexual exploitation.
“The new structures enable us to work closely with our partner agencies in a much more cohesive way than before to ensure better protection and safeguarding for children and young people.”
The office said the PSNI has also revised its Missing Persons Protocol, a joint policy with the health and social care authorities.
“This protocol is designed to support effective collaborative safeguarding responses by the PSNI and social services in respect of children who run away or go missing from their homes or care placements and builds upon developments in our knowledge and experience,” Mr Clarke added.
Last year, a separate review into the issue concluded that sexual exploitation was a growing threat to young people in Northern Ireland.