Yes, we have. I've seen her parents and brother on TV a number of times since Natalee disappeared. I really feel for them--they will probably join that large club of parents who never find out what happened to their missing sons and daughters.
Amy's case was a little different. Their ship had left Aruba and was at sea when Amy went missing. At that time, someone may have been holding her in a cabin and taken her off at the next stop (which I believe was Curacao).
What about Claudia Kirschhoch, missing from Jamaica? Or any others? I didn't know about these two until today.
http://findclaudia.homestead.com/