'Wow, I am your first comment, thank you for the add!' is referring to writing on somebodies my space account. So would it be okay to say:
'Caspita! Sono il tuo primo commento (this sounds awkward to me!), grazie a te per l'add.
I don't understand "add" here either. I've never heard it used as a noun in English, yet is used here as if it were one. I think the writer was trying to say either "advertisement" or "addition" but which is unclear from the context.