Pinging people on chat or in comments is rather helpful. Let us leave aside the fact that strict grammar is often not necessary in such places. Rather, out of curiosity, what would be the correct way to do it?
Firstly, I thought a plain comma ought to suffice.
@Someone, help me! You are my only hope.
Then the apparent became obvious. Since the meaning of '@' is at, then the following might be more appropriate.
@Someone: We have a problem.
Or would perhaps even an em-dash work?
If the construct is at the middle or end of a sentence, how to proceed?
That'll do [*] @Someone [*] that'll do.
Good morning [*] @Someone!
Here '[*]' stands for an unknown punctuation mark.
It is clear that in a few cases taking '@Someone' ~ 'Someone' is the only option.
Elementary, my dear @Someone.
The other instances are, to some extent, more arguable.
Which option do you think is best?
P.S. As per 'Does other punctuation affect the notification?', punctuation generally does not interfere with the underlying process.