Madeleine McCann's family have said the identification of a new suspect is a "significant development" in the case.
A spokesman for the family added that they have never given up hope.
Madeleine was just three when she disappeared from her family's holiday apartment in Praia da Luz, Portugal, on the evening of May 3, 2007 – sparking a huge police hunt that lasts to this day.
Last night police searching for Madeleine said they have identified a new suspect and even published two phone numbers they believe may be linked to her disappearance.
The Metropolitan Police revealed the German prisoner is known to have been around Praia da Luz on the Algarve coast at the time Maddie vanished on May 3, 2007.
Following the news, Clarence Mitchell, a spokesman for the family, told BBC radio: "Kate and Gerry do feel it's potentially very significant."
He added: "They've never given up hope that she may still be found alive but they are realistic.
"Whatever the outcome of this particular line of investigation maybe, they do need to know what happened to their daughter to find peace and to bring whoever is responsible to justice."
Police have not named the German national, 43, who is described as white with short blond hair, possibly fair, and around 6ft tall with a slim build.
A half-hour phone call was made to his Portuguese mobile phone around an hour before Madeleine is believed to have gone missing.
The suspect, who is in prison in Germany for an unrelated matter, has been linked to an early 1980s camper van – with a white upper body and yellow skirting, registered in Portugal – which was pictured in the Algarve in 2007.
Scotland Yard said he was driving the vehicle in the Praia da Luz area in the days before Madeleine's disappearance and is believed to have been living in it for days or weeks before and after May 3.
He has also been linked to a 1993 Jaguar XJR6 with a German number plate seen in Praia da Luz and surrounding areas in 2006 and 2007.
The day after Madeleine went missing, the suspect got the car re-registered in Germany under someone else's name, although it is believed the vehicle was still in Portugal.
Both vehicles have been seized by German police. Scotland Yard is launching a joint appeal with the Federal Criminal Police Office of Germany (BKA) and the Portuguese Policia Judiciaria (PJ).
Scotland Yard is launching a joint appeal with the Federal Criminal Police Office of Germany (BKA) and the Portuguese Policia Judiciaria (PJ), including a £20,000 reward for information leading to the conviction of the person responsible of Madeleine's disappearance.
Det Chief Insp Mark Cranwell told reporters on Wednesday he was taking the "really unusual" step of releasing two mobile phone numbers as part of the appeal.
The first, (+351) 912 730 680, is believed to have been used by the suspect and received a call from another Portuguese mobile, (+351) 916 510 683, while in the Praia da Luz area, starting at 7.32pm and ending at 8.02pm on the night of May 3 2007.
Madeleine is believed to have disappeared between 9.10pm and 10pm that evening.
The caller, who is not thought to have been in the Praia da Luz area, is not being treated as a suspect, but is said to be a "key witness" in the case.
"Any information in relation to these mobile numbers during the spring and summer of 2007 could be critical to this investigation," said Mr Cranwell.
The Operation Grange incident room can be contacted on 0207 321 9251 or [email protected]