Your new subscriber is more engaged with you now than they EVER will be again. Now is the time to ask them to help spread the word. The more of this work you do for them, the better. Give them buttons, and make the ask!
Also!!! If you use a double opt-in (you should), this page is where you say, "make sure you head on over to your inbox and confirm your subscription."
Social proof matters! Share counts will make other people more likely to share your stuff.
(If you have it. If you don't, hide the numbers.)