I just got on to play Diablo III and all my characters are gone. I even have the Necromancer expansion and NOTHING all my characters are gone 
Be sure you have the right region selected (i.e. North America) in your Battelnet client app.
Also make sure you are using the correct email.
I don’t see any profiles in any region
If you login to Diablo III and cannot find your old heroes, it is possible you have logged into the wrong region.
It is possible that the account is under another email than the one you remember. Try logging in with another email address to see if you can access the account.
In case you are playing on console, read this: