Chancellor Gordon Brown has had several telephone conversations with the father of missing Madeleine McCann, a family spokesman in Portugal confirmed.
Mr Brown offered both parents Gerry and Kate "his full support" in their efforts to find the four-year-old, who vanished on the night of 3 May.
Police have issued a description of a man seen on the night Madeleine was taken from the Praia da Luz apartment.
In a statement, Mr McCann said the sighting of the man was "significant".
A spokesman for the McCanns said: "I can confirm that telephone conversations have taken place between Gerry McCann and Chancellor Gordon Brown.
"During them, Mr Brown offered both Gerry and Kate his full support in their efforts to find Madeleine, although details of the conversations will remain private.
"The conversations took place against the background of the chancellor's earlier offer to help when he met and spoke to other members of the McCann family in the UK."
Police officers in the Algarve said the man they want to question was "carrying a child or an object that could have been taken as a child".
Portuguese police went public with the description after pressure from the McCann family to move the investigation on.
BBC correspondent Steve Kingstone in the Algarve said it was the first time the police had given a detailed description of a man they wanted to speak to.
But it is not known how long detectives had known this information or whether they believed the man abducted Madeleine, he added.
The man is said to be white, 5ft 10in, medium build with short hair, and wearing a dark jacket, beige trousers and dark shoes.
The BBC's correspondent said police were publicly playing down the similarities between the man described and the only official suspect in the case, Robert Murat.
Mr Murat denies any involvement in Madeleine's disappearance.
Madeleine's parents said they were pleased that there "appeared to be a new development".
On Friday the McCanns told the BBC of the guilt they felt at not being with their daughter when she was abducted.
Gordon Brown has offered to help the McCanns find their daughter
They said they were experiencing "every parent's worst nightmare" and loved her "more than anyone could imagine".
Madeleine, from Rothley, Leicestershire, was abducted from her bed in the Algarve resort as her parents ate dinner at a nearby tapas restaurant.
The McCanns said criticism of them for leaving her in the bedroom was "hard to deal with", but insisted that thousands of other people would have done the same "in such a safe resort".