I agree...there are so many search sites! Within houses, gardens, industrial estates, sheds, woods...it's bizarre! Unless the people arrested are giving them the run around.
Or maybe they are treating it as an abduction and think she is being held somewhere against her will in that area. It is rare that that's the case - occasionally you hear of it in America or elsewhere but in the UK I can't recall that happening. Stranger things have happened though I guess but just more used to missing persons either being the worse possible outcome of the persons run away.