User to User requests appear in the "App Center" area of Facebook. You can find that in the left-hand sidebar in the "Apps" section. Click there and your requests should show up.
The next big release (due out in October) should have a way to send Application Notifications to users that show up in the area you show in your picture. Application Notifications are from your site to the user, not from user-to-user, like invitations.
I hope that helps, but if you have other issues, or need anything else, let us know.
Thanks,
Alex
customizing request message
