I take it this is a sensible question. The best step you can take is to buy The Sun Newspaper on a Thursday. In that particular edition they have a "Where are they now"? section where you can list all details of your sister's full name, and last known whereabouts. Please give as much detail as you can, including her full maiden name, and also married name. I understand that quite a few missing people have been found in this way. Anyone who knows her location now, should write to you via The Sun, and that is how you'll get your replies.