Metropolitan Police forces have come under criticism for lack of training when dealing with missing children and domestic violence victims.
In a report released today, Her Majesty's Inspectorate of Constabulary (HMIC) said staff training needed to be improved, with a better understanding in repeated instances of absent children.
HM Inspector of Constabulary Zoë Billingham, who led the inspection, said: "Victims of crime and anti-social behaviour who are vulnerable in some way are in greatest need of the police's protection and support, but HMIC's inspection found that most forces require improvement in how they protect and support them."
She added: "Whatever the overall judgment we came to, we know that there is hard work carried out by dedicated police officers and staff in every police force."
This inspection examined how forces respond to those who are vulnerable in some way, with a focus on missing and absent children and victims of domestic abuse.
It also looked at how well prepared they are to tackle child sexual exploitation.
HMIC has said police forces must improve the service they offer to vulnerable victims, as even the smallest failures can have tragic consequences.
The Metropolitan Police told Getwestlondon: "We recognise the continued challenge of dealing with those who inflict this damaging behaviour upon others.
"We know crimes inflicted against vulnerable victims often go unreported and we encourage people to come forward, knowing that we will support them with professionalism and compassion.
In the last year, Met Police Service received over 98,000 reports of people going missing and said the forces take this matter very seriously.
West London charity Missing People, who recently held a Carol concert where the family of Alice Gross sang a song composed by the murdered teen, said all missing children are vulnerable and need help to stay safe.
A spokesperson for the charity said: "Many children go missing to escape violence and abuse but once missing they are hidden from help and at serious risk of harm and crimes including sexual exploitation.
"The police should not be left to do this job in isolation – local authorities and other agencies must play a role in preventing people of all ages going missing and in making sure help is available and delivered when they return in order to stop them going missing again."
