The team of volunteers is set to examine 19 sites around Saddleworth Moor. They are relying on evidence from witnesses who have come forward with information they hope could find the boy's remains.
David Jones, who is director of the International Rescue Training Centre in Wales, said: "It's a large area. If we were to work this area as we do, this could be a 12-month search on just this one area.
"If we're looking at all the sites we've been given, we could be here for months, years – it just depends which area we're given and where we can locate a body."
He said he hopes his joint team, also made up of rescuers from Global Rescue Services, will be able to find Keith's improvised grave.
Officers, who spent five decades looking for the 12-year-old's remains, made a massive last effort in 2008 but turned up nothing.
Keith's mother Winnie Johnson, 76, has been unable to hold a funeral for her son as his body has never been found but earlier this month she paid tribute to her son at a special memorial service, being held in lieu of a funeral.
The volunteers are using satellite technology to track their movements and catalogue the search areas, which are marked out into squares of 20 metres by 20 metres and methodically covered by specialist dogs and handlers.
Asked how the project was being financed, Mr Jones said: "At the moment it's not. They have started up the Keith Bennett Appeal, I believe, and they will be raising funds for whatever they need."
Keith is the only one of the Moors victims still to be found.
Ian Brady and Myra Hindley's other victims were Pauline Reade, 16; John Kilbride, 12; Lesley Ann Downey; and Edward Evans, 17.