The San Francisco social networking site, Piczo, which focuses on teens and photo-sharing, is boasting 17 million registered users. It has raised a total of $7 million (scroll down), according to GigaOM’s Liz Gannes, who brings us an update on the relatively closed, privacy-conscious site. (We’d reported earlier only $4 million raised). Sierra Ventures and Catamount Venture are the backers.