Hi Sylvia,
I've always had pretty good luck with
AT&T's Anywho lookup. White pages come in handy for people, which is what I think you are after. Plus, it's free!
Another thing, if you/they haven't done this, is to put "Return Address Requested" or "Return Service Requested" on the envelope. This link to the
US Postal Service may help explain the different wording one can put on the outside of an envelope and what will happen when you do.
Can ya tell I had to hunt down former employees before?
HTH a bit,