Police have been criticised for "unacceptable delays" in dealing with a distraught mother's emergency calls in Bolton, Greater Manchester.
She reported that her missing 15-year-old daughter was at risk of sexual grooming and exploitation in April last year.
The police watchdog has told the force to apologise for taking 10 hours to respond to one of her 999 calls.
Ch Supt Steve Hartley said lessons "will be learned" from the report.
The young girl had gone missing from home on five occasions between June 2008 and March 2009.
On 17 April 2009 her mother made a 999 call at 2248 BST to report her daughter was missing.
She then contacted the police again at 0249 BST and told them she believed the teenager was at risk of being sexually assaulted.
The Independent Police Complaints Commission (IPCC) said the second call should have been treated as high priority.
However, it took police six hours to respond due to "resourcing difficulties".
The girl returned home the following day and later told police that she might have been the victim of a sexual offence.
The IPCC also found there were delays in ensuring forensic evidence was secured when the girl returned home.
Despite the late response, the IPCC said that it "would have been unlikely" that any sexual activity could have been prevented and no individual officer had committed misconduct.
IPCC Commissioner Ms Naseem Malik said: "Although it is appreciated resources were seriously stretched and officers were deployed elsewhere dealing with serious incidents, a delay of more than 10 hours in responding to those concerns was unacceptable.
"The investigation concluded the incidents involving the daughter would have occurred even if officers had responded quicker.
"But the delay must have affected the mother who was clearly extremely worried and wanted police help."