Good questions, Susan. For instance, as best I can tell from examining the first few threads you listed:
Help: Where is Debbie McClatchy?
Janet Jones - Where did she go
Where IS Danny Spooner?
Where's Tommy Sands?
Where's Enda Kenny gone ?
Where's Whizz? (Wizz Jones)
Whereabouts of Bob and Melody Thomason
Glenn Yarbrough, where is he now?
Cory & McKelvey...where are they now?
Tom Taylor ? Did Woody---Where is he?
MARY O'HARA - where is she know?

what appears to be good information was given in response. Ostensibly, the cases were solved. But the person who posted the original question may not have ever indicated whether contact was actually accomplished (if that was the goal.)

It would seem a starting point would be to have a monitored thread not unlike the missing tunes thread in which, once the tune is reunited with the song, the entry is removed from the list. But in the missing persons threads, it is often impossible to know if the search is really over without input from the original poster.