How does Pinterest make money (Facebook)

[robertpasa]

...since I don't see any ads on their pages?

They don't. Venture capitalists rain money down upon them out of the hope that someday it becomes a profitable enterprise.

The plan? Promoted pins - aka selling ads. It remains to be seen if that is worth enough to justify a multi-billion dollar valuation.

[Shutout]

Wasn't facebook ad free for awhile?

It's the new thing... growth first, profit later.