By all means congratulate him.
i always congratulate my friend when she passes her maths test The coaches met at midfield to congratulate each other. I would like to congratulate you for writing this very excellent question. You want me to congratulate WHO? Yes ma'am, I am looking for a nice greeting card here because I want to congratulate my cousin on his splendiferous addition to the family tree.
You can't congratulate them specifically for their birthday, but on their page there is a box with a link you can click to congratulate them. If you want to make it clear that you congratulated them because it was their birthday, PM them and say something like, "Congrats of your birthday!"
Way to go
The noun form of "congratulate" is "congratulation."
You can congratulate anyone even if there are not your friend. You just go to their page and click congratulate.
Congratulated is the past tense of congratulate.
I would like to congratulate you on your exemplary example sentence.
Congratulations is a noun.
I want to congratulate a business associate on the birth of his new grandson and I am just wondering how to say it?
I'd like to congratulate you on already answering your own question.
It might be seen as rude to congratulate. It is best to leave it alone and allow him to deal with it. However, if you have a good relationship, it is fine to congratulate.