Gee, it seems as though I've read about such services but I have no idea where and don't really have any idea where to start looking.

Anyway, 2 ideas:

1) Depending on where your traveling you might try a Hostel. Some are nice and some are nasty! But they always lend themselves to meeting others and establishing friendships.

2) Try a site that Chris recommends by a carreer flight attendant.
www.travelaloneandloveit.com