Scotland Yard urged Portuguese authorities to reopen the search for Madeleine McCann today as detectives said there were 195 potential leads to finding her alive.
The detective leading the Metropolitan Police review said the case could still be solved before officers released a picture of what she might now look like as a nine-year-old.
Detective Chief Inspector Andy Redwood said he believed her disappearance was a stranger abduction, as he said there were 195 "investigative opportunities".
Police refused to say what evidence they had uncovered to suggest Madeleine was alive.
Mr Redwood confirmed that his team of more than 30 officers involved in the case had been out to Portugal seven times, including a visit to the family's holiday flat in Praia da Luz.
It will be five years ago next week since the three-year-old went missing as her parents, Kate and Gerry McCann, dined with friends nearby.
A spokesman for the McCanns said the family were pleased with the image.
Mr Redwood said his 37 officers had dealt with 40,000 pieces of information but the "primacy still sits in Portugal" in the attempt to find her.
Commander Simon Foy said: "Most significantly, the message we want to bring to you is that, on the evidence, there is a possibility that she is alive and we desperately need your help today to appeal directly to the public for information to support our investigation."
Mr Redwood said "evidence that she is alive stems from the forensic view of the timeline" that there was the opportunity for her to be taken.
Investigations show "there do appear to be gaps", he added.
The investigative review was launched last year after a meeting between former Met commissioner Sir Paul Stephenson and the Home Office.
Detectives in Portugal are also understood to want the case reopened but must gain judicial approval via the courts.
Mr Redwood added: "So far, I have conducted seven visits to Portugal. Two of those visits have been at senior level, one of those visits was a visit to the actual resort itself and four of the other visits were directly face to face with the review team."
Mr Foy said: "We have been collaborating with Portuguese authorities, we have briefed the ambassador.
"It's a complex situation in Portugal and we hope that the Foreign Office will help us with that."
Mr Redwood added: "We would like the case to be reopened, our case is clear... (But) I should stress quite clearly that the decision is in Portugal."
He said this did not mean that his review of the case was toothless.
"What we are not doing is just passively passing through material. We are actively seeking to bring closure in this case."
There is a "timeline of opportunities" indicating the little girl was taken "as a criminal act", he added.
The new image was created in "close collaboration with the family" ahead of the fifth anniversary of her disappearance on May 3.
The review team has compiled and reviewed material from three separate strands - the Portuguese investigation, inquiries in the UK and the work of private investigators.
The information gathered totals about 100,000 pages.
Mr Redwood said: "From the outset we have approached this review with a completely open mind, placing Madeleine McCann at the heart of everything we do.
"We are working on the basis of two possibilities here - one is that Madeleine is still alive, and the second that she is, sadly, dead.
"Based on the former we are releasing the age progression image today with a specific appeal.
"If you know where Madeleine McCann is now or you have new direct information or evidence about what has happened to her then please contact us."
Anyone at the resort of Praia da Luz between April 28 and May 3 2007 "particularly in the vicinity of the Ocean Club" is asked to come forward if they have not already spoken to police.
:: Potential witnesses are urged to call 0800 096 1011 within the UK or +44 207 1580 126 from outside. Crimestoppers can be contacted anonymously on 0800 555 111.