LONDON — British police say they have launched a full investigation into the disappearance of Madeleine McCann and want to trace 38 “persons of interest” in the case.

Detectives say it’s possible that Madeleine, who vanished from a Portuguese holiday resort six years ago, is alive.

Scotland Yard said Thursday that 12 individuals of interest are British, and the rest are from a variety of European countries. The force says it is working with governments across the continent to find out more.

Scotland Yard told BBC News that “new evidence and new witnesses” in the case caused it to open a formal investigation into the girl’s disappearance.

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Madeleine was almost 4 when she disappeared in Portugal in May 2007.

She disappeared from her family’s holiday flat in the Algarve resort of Praia da Luz, as her parents dined out with friends at a nearby restaurant.

Portuguese authorities dropped their investigation into her disappearance in 2008, but Scotland Yard started a review in May 2011, after Prime Minister David Cameron responded to a plea from her parents.

Her parents, Gerry and Kate McCann, said the shift from review to investigation was “a big step forward.”

The case has generated intense media interest.

British officers who have spent two years reviewing the initial investigations into her disappearance have found “new findings and new witness evidence,” a police statement said.

Detective Chief Inspector Andy Redwood said police “continue to believe that there is a possibility that Madeleine is alive.”