These are just some of the sites that I have found.  I am
sure there are more out there. 

I am listing some of these sites below...

Class Ring Finder
This site is free.  All you have to do is register, then put in what you are looking for, and if you are offering a reward.  If you enter an email, you will be contacted.

Lost My Ring
This site charges $1.99 to sign up, and $6.99 per year.

Treasure Hunting
Must register, but registration is free.

Treasure Net

Class Rings Lost & Found - Facebook Group

Jostens.com Lost & Found Rings

The Ring Finders

Lost And Found Class Rings