“Happy birthday Madeleine. Still missing. Still very much missed. Still looking. For as long as it takes,” they said in a post on the official Facebook page of the Find Madeleine Campaign.

“We love you and we’re waiting for you. We’re never going to give up,” they added in the message accompanied by a YouTube video with photos of the missing girl.

Earlier this month, Madeleine’s family held a vigil to mark 16 years since her disappearance while on holiday in the Algarve region of southern Portugal.

Madeleine went missing from her family’s holiday apartment in Praia da Luz on May 3, 2007, days before her fourth birthday, as her parents dined with friends at a nearby restaurant.

Her disappearance triggered an international manhunt, but no trace of her has been found and no one has been charged over her disappearance.

A court in Brunswick, Germany, said last month it did not have the jurisdiction to hear the case against the prime suspect in the McCann case for unrelated sexual offences because his “last known address” was in another German state.

The suspect is currently serving a seven-year sentence for raping a woman in the same area of the Algarve where McCann went missing.

Despite the court’s decision, the Brunswick prosecutor’s office said it would continue investigations related to the McCann case.