HARRY POTTER AUTHOR J.K. ROWLING has joined the campaign to find missing British child MADELEINE MCCANN, by asking stores that stock her new book to put up a poster advertising her plight. Four-year-old Madeleine was snatched from a holiday resort in Portugal in May (07). Rowling has vowed to include a poster with a picture of the child with every consignment of books - so bookstores around the world can spread the word about her disappearance. The author says, "I fervently hope that posters displayed prominently in shops all over the world will help find Madeleine MCCann and help raise the profile of the many other missing children in different countries."