Imessage doesn't send or receive and after I try to send them an imessage it fails and says they are not registered with Imessage.

Imessage doesn't send or receive and after I try to send them an imessage it fails and says they are not registered with Imessage. I have tried resetting my network settings, making a new apple id and signing in with that, restarting my ipod touch 5th gen and other things. Any suggestions would be greatly appreciated.