The parents of Madeleine McCann were given a deeply moving letter from the family of a missing Spanish boy yesterday urging them not to give up looking for her.

The note was given to the British couple during their visit to Madrid to publicise their four-year-old daughter's disappearance.

It was written by the parents of seven-year-old Yeremi Vargas who disappeared outside his home in Gran Canaria in March.

They told Kate and Gerry McCann to keep strong and never lose hope because "that is what is left to us".

It is now 30 days since Madeleine was snatched from her bed as she slept in the Algarve resort of Praia da Luz while her parents ate at a tapas bar nearby.

Yesterday, they spoke of their hopes and fears about what has happened to their daughter during a series of interviews in the Spanish capital.

They said they desperately want to believe her abductor is someone who simply wanted a daughter of their own and would never harm her. They admitted they have also thought about the worst - that she may be in the hands of a paedophile or never found - but insisted they would not believe anything other than she was safe and well.

Mr and Mrs McCann, both 38, are travelling across Europe to raise awareness about their daughter's plight.

Referring to Yeremi's disappearance, Mr McCann, a Glasgow-born cardiologist, said: "I think it is at least worth exploring the possibility that Madeleine's disappearance should not be considered in isolation, so putting it into context with other disappearances in the Iberian peninsula, even the Canary Isles as well."

Back in Portugal it was claimed yesterday that DNA from a mystery "sixth" person was found in the bedroom where Madeleine was abducted.

The Portuguese police, Policia Judiciara, have handed the sample to the national forensic laboratories, according to local newspaper 24 Horas.

It does not match the DNA of Mr and Mrs McCann or their three children, the paper said. Neither does it match that of the only named suspect in the case, property developer Robert Murat, the paper added.

It quoted a source from the laboratory who said: "There is a new suspect. There is DNA which does not correspond to the family. It is an important step in the investigation but the truth is that the DNA collected does not have a name ... we cannot make any connection between the material collected and the suspects which we already have."

It also emerged yesterday that 1000 photographs have been uploaded to a website set up to try to identify Madeleine's abductor following an appeal to holidaymakers who were at the Ocean Club Resort at Praia da Luz in the two weeks before Madeleine's disappearance to submit images.

Elsewhere, hundreds of yellow balloons were released in Glasgow and Northern Ireland yesterday as a "symbol of hope" that Madeleine will be found alive and well.

John McCann, the child's uncle, said he hoped someone with "vital knowledge" of her abduction or current whereabouts would be persuaded to inform police after finding one of the balloons.

He was speaking as 400 yellow balloons were released by pupils at Bankhead Primary School in Knightswood, Glasgow where Diane, his wife, is a teacher. Tied to each balloon was a tag with the Madeleine appeal information, including the UK and international telephone numbers for people to pass on any relevant information.