A new book written by Kate McCann entitled "Madeleine" is due for release on May 12

LONDON ? The parents of missing girl Madeleine McCann were Tuesday to mark the fourth anniversary of her disappearance as they prepared to release a book to boost dwindling search funds.

Gerry and Kate McCann, from Leicestershire, are expected to spend the day with family and friends as they remember their daughter who went missing on a family holiday to Portugal in 2007.

Gerry McCann warned in November that a search fund set up by the couple, which once stood at two million pounds, was due to run out at any time.

A new book written by Kate McCann entitled "Madeleine" is due for release on May 12, and proceeds from the expected best-seller will go towards the search efforts.

The McCanns hope details contained within the 384-page book will jog the memory of anyone who may have information about the disappearance.

Madeleine went missing from a holiday apartment in the Algarve resort of Praia da Luz on May 3, 2007, a few days before her fourth birthday, as her parents and their friends dined at a nearby restaurant.

"It will be a private day marked with family and friends. The anniversary is normally a very low-key occasion at home for them," family spokesman Clarence Mitchell said.

The McCanns were named as official suspects in her disappearance in September 2007 but this was lifted in July 2008.