Self-proclaimed "vigilantes" posing online as underage girls to meet alleged paedophiles could threaten successful prosecutions, say police.
Members of the 'Letzgo Hunting' group, which was set up in January, have so far met nine men they claim are would-be paedophiles, after luring them to meeting places by posing as girls, aged 12 to 15.
Leicestershire Police said they had arrested four people as a result of information supplied by the group but added such "naming and shaming" tactics "can seriously affect the chances of success in court" and deny victims justice.
Child welfare and protection group the NSPCC said tracking down paedophiles must be done "by the proper authorities".
The group works by arranging meetings with the men in public places, then confronts them with a video camera and tries to question the person on their reasons for turning up, before posting the footage online. Its leader, a parent who gave his name as Scumm Buster, told the BBC's Radio Five Live: "Our main aim is to make sure of who these people are. We don't encourage violence at any point, we don't want violence."
He added: "We are vigilantes definitely. We're not working within the law but we're not a vigilante lynch mob, we're not there to hurt anybody, we're there to get an explanation."
He said the group's footage is always passed to the police and is removed from the group's website from the moment the police start an investigation, to avoid prejudice to any possible legal proceedings. The founder member, who said he has worked previously in the security industry, said the group of three men and a woman were all parents of varying ages saying - "that's obviously why we do what we do".
A Leicestershire Police spokesman said paedophile investigations were also carried out "within the strict rigour of the law" to ensure the best chance of a successful prosecution, adding the work was a 365-day-a-year, 24-7 operation.
The spokesman added: "Unfortunately, these kinds of public naming-and-shaming activities can actually have a negative affect on victims of child abuse. While we understand the strong feelings that motivate this kind of activity, it can seriously affect the chances of success in court, preventing victims from getting justice and increasing the chances of offenders walking free. It also fails to take into account that many victims of child abuse are children or family of the offenders thus bringing extra distress to innocent people and affecting our ability to safeguard victims."
He went on: "The best thing people can do, if they have evidence of child abuse or paedophile activity, is report it to the police, Crimestoppers or Child Exploitation and Online Protection Centre so that we can conduct a thorough investigation and make sure measures are put in place to ensure the safety of any potential victims."