Does a Comma Go After Thanks?

If you are telling someone “thank you” directly, you always need a comma after “thank you.” This is the most common way of using the phrase, so in most cases you will want that comma. You should also put a comma or a period after “thank you” if it's the last part of a letter or email before your name or signature.

Is it thanks John or thanks John?

Thanks John - you're the one who is saying "thank you" to John. For example, when John gave you something and then you say, "Thanks, John!" Thank John - someone else is asking you to thank John for him/her.

Is there a period after thank you?

When it comes to punctuating "Thank you" you can either use a period "." or an exclamation point "!", there's really no right or wrong choice here (as long as you don't use a question mark).