I editted two of my original posts in the "Request a Teen" forum to try and fix them so a thumbnail would show in the forum list. Its been over 2 hours and the Forum is still showing "LINK" and it goes to the old URL, not the new ones. According to the Help, editting should have fixed this. Thanks.

It can take anything from 2 - 24 hours before new link produces new thumb-preview.

That's because this facility is on a separate server.  So please be patient.

Moreover, not every link will give you a thumb.  That's just a matter of trying, wait and see.