The parents of Madeleine McCann have urged people to "rack their brains" and come forward with information after police said they had a new focus on the investigation.
Two new e-fits of a man were broadcast in a fresh television appeal, while Scotland Yard said they had effectively ruled out a previous key sighting of a different man carrying a little girl.
The senior investigating officer, Detective Chief Inspector Andy Redwood told BBC's Crimewatch programme one reading of the evidence is that the kidnapping had "the hallmarks of a pre-planned abduction that would undoubtedly have involved reconnaissance".
Viewers were shown a pair of images of a man with dark hair, which are based on descriptions from two witnesses who were staying in Praia da Luz, Portugal, when the three-year-old went missing on 3 May 2007.
Mr Redwood said during the show that two independent callers had put forward the same name for the man and another caller had given a name of a man who was known to be in Portugal at the time of Madeleine's disappearance.
In a live interview, Gerry McCann praised the Metropolitan Police for finding new information to take the investigation forward, saying: "I think we're feeling hopeful and optimistic.
His wife Kate said: "It doesn't matter how much heartache we put ourselves through, so long as we get the result that we need."
Urging viewers to call the show, Madeleine's mother added: "Please, please have the courage and confidence to come forward now, and share that information with us, and you could unlock this whole case, so please."
Mr McCann said people should find hope from recent cases in which abducted children had been found after long periods of time.
Madeleine disappeared from a holiday apartment as her parents dined at a nearby tapas restaurant with friends.
Scotland Yard said work by detectives has given them a far greater understanding of the times when the abduction could have taken place.
The witnesses have described the man in the e-fit as being white, aged between 20 and 40, with short brown hair, of medium build, medium height and clean shaven.
One of the main priorities for the investigation is being able to identify the man, police added.
Detective Chief Inspector Andy Redwood, the senior investigating officer, said that while this is far from being the only line of inquiry, it is of "vital importance".
"Whilst this man may or may not be the key to unlocking this investigation, tracing and speaking to him is of vital importance to us.
"We have witnesses placing him in the resort area around the time of Madeleine's disappearance."
He said that detectives have been able to "make massive steps forward" by drawing together all the material gathered to date and reviewing it as a whole.
"Praia da Luz is a popular holiday destination for many nationalities so our requests for help need to be repeated in many different countries.
"I will be travelling to Holland, Germany and Ireland to seek the support of the public there."
He added: "Portugal is a key country for us to trace any outstanding witnesses and our appeals will be repeated there."
Former Metropolitan Police detective Jacqui Hames said investigators are providing new detail on the whereabouts of people in the area when the little girl went missing.
Speaking on RTÉ's Today with Sean O'Rourke, she said: "It would appear that the officers have meticulously gone over interviews of people who were brought forward at the time and reassessed what they said.
"It would appear, we'll hear more in Crimewatch tonight, that they have come up more theories about what might have happened during that 90 minutes when Madeleine was on her own, but also where everybody else was.
"There may have been discrepancies in what people originally said," she added.