I would never.  In the entire world, there are only two people with my first and last name: me, and my dad's second cousin's wife.  Someone who sees my Facebook can easily find out where I live, who my family is, what high school I went to, what my grades were in middle and high school, and more.  From that information, they could easily come to my house and hurt me or someone I love.  I would never take that risk.  If I meet someone online, I have to know them for years and years before I trust them enough to tell them my last name or let them be my friend on Facebook.  In fact, there has only ever been one person from the Internet who earned that trust in my entire life.

I won't even reveal my surname to anyone over the internet. I have several different emails I use for things like signing up to this site; I keep my personal email separate. I was extremely reluctant to upload my photo to this website in the first place!

que paranoico el de arriba.

No and I would not either. Facebook is only for my friends, relatives and acquintaces. 

I don't share my facebook, I share my Skype. I mean, I'm here to practice languages so I use Skype for that. I've never thought about sharing my Facebook account and none have asked either.