Self-styled paedophile hunters have been urged to “leave it to the professionals” as police bolster covert efforts to tackle online grooming.
Senior officers said vigilante groups such as Dark Justice or The Hunted One could put child abuse investigations at risk.
The warning comes as the Home Secretary, Amber Rudd, announced £20m funding to extend an initiative where undercover detectives operated in internet chat rooms and forums used by suspected offenders.
Forty-three people were arrested and 19 were charged as a result of the year-long pilot in eastern England, led by Norfolk Police, and officers believe they have safeguarded at least 25 children.
Detective Superintendent Steven Woollett, of the Kent and Essex serious crime directorate, said the Government's cash injection to extend the scheme to the rest of England and Wales would make a “real difference” in helping to identify suspects and protect children.
He declined to be drawn on how police work in an online realm that has increasingly seen members of the public take action to trap child abusers themselves.
Tyneside-based duo Dark Justice claim on their website to have helped snare 104 sex crime suspects, leading to 50 convictions, while a sting operation by the group known as “The Hunted One” descended into violence as they ambushed a man who sent sexual messages to a decoy account.
Their target, Mirza Beg, 29, was jailed at Maidstone Crown Court this month for 40 months after he turned up with condoms at the Bluewater Shopping Centre in Greenhithe, near Dartford, Kent, believing he was meeting a 14-year-old girl.
Mr Woollett said offenders might become more evasive as a result of the groups' actions.
“My personal view is, as much as they may be well intended, there is the potential to hinder police investigations,” he said.
“My message to them would be we are professional law enforcement - leave it to the professionals.
“I would have to admit they've had some success - we need to balance that success against the potential harm by heightening the awareness of individuals.
“I think with all strands of criminality, those people responsible become more aware and more cute around their business.”
But he added: “I would not be able to say vigilante groups have increased that.”
His message was echoed by National Police Chiefs Council lead for child protection, Chief Constable Simon Bailey, who said police are arresting more than 400 offenders and protecting more than 500 children every month.
He said: “This increase in our undercover capability will send a clear message to so-called paedophile hunters: if you have information about child abuse, tell the police.
“Don't try to take it into your own hands, you could undermine police investigations creating more risk for the children we all want to protect.”
The funding, through the Police Transformation Fund, will see police forces jointly monitor forums and share intelligence in collaboration with the National Crime Agency Child Exploitation and Online Protection command.
Ms Rudd said: “Child sexual exploitation has a profoundly devastating impact on the lives of its victims, and it's a national policing priority to take on the threat it poses.
“We believe this project has shown early promise in tackling these complex crimes through an innovative approach.”