Well, finding a name might be a bit difficult.
A relatively solid claim can be made that "social networking" is basically little more than a Web 2.0 face-lift for what used to be called online communities and clubs.
Yes, the technologies have greatly developed, making the general feel of the "community" different, but we're still basically dealing with offering people the opportunity to electronically mingle with like-minded people. And among those clubs were many that were devoted to sharing photos of what many would consider porn.
Things have changed, not only technologically, since then. Though it might make sense that even when it comes to porn people might choose to share their collections, or discuss them with others, people today are considerably more concerned about what they keep on their hard drives, and what they share with others. I greatly doubt that a group with a name along the lines of "porn lovers online", or "pedophiles 2.0" would be the sort of adult community that anyone would be comfortable joining, let alone listing their membership in such a group on a CV.
Go to: The plain brown paper envelope column.