Comma needed?

AnonymousHi john I miss you too.

Yes, you should put a comma after John. The comma just adds a short pause, and a small separation between "Hi John" and "I miss you too". You could also use a period, which creates a longer pause and more separation between the sentences.

You actually need two commas, a semicolon (or a period) and a capital letter:

Hi, John; I miss you, too.
Hi, John. I miss you, too.

I suggest the second.

Mister MicawberHi, John; I miss you, too.
Hi, John. I miss you, too.

I respectfully disagree. I believe this is a STYLE issue, and I feel those commas are inappropriate.
I have seen this way of writing occasionally (I have a friend who uses it, and she is quite well-educated - she would never try to thoughtlessly split an infinitive), but I believe it

KrisBlueNZ

Mister MicawberHi, John; I miss you, too.

Hi, John. I miss you, too.

I respectfully disagree.

I agree with you.

By the way, I don't think that commas always denote pauses.

But in any case, those sentences just don't need commas, in my opinion.

And they also look very cluttered with

It is fine to express your opinion here, Kris, but not to the extent of belittling others'. I am one of those modern literate people to whom you have an obligation, and my opinion has been given above, as was yours before that.