I just dealt with this same issue. I wanted to give a friend a link so she could sign up with HP and I was having a heck of a time figuring it out. Here's how I found the link. 'Hope this helps. I don't think you'd use the referral track on Twitter and I don't see how you could on Pinterest. Anyway, to get the link:
1) go to account
2) go to earnings
3) to to referral trackers
4) I created a tracker called ChrisHughBuddy
and then the next part, where I tell you how to do the link, I can't seem to do that here cause i'm getting an error message about the link. Let's try some asterisks.
Just ignore the asterisks and use your own referral tracker. Now, for full instructions, without asterisks, check out my blog. it's called serpiethespider. it has its own domain. so it's w w w -dot-serpiethespider-dot-com