Facebook works on a spiderweb network model...
You have a list of friends. You send a link to them.
Your friends each have their own list of friends. They send the link on to them.
Their friends also each have their own list of friends and they send the link on...
Ok, a lot of the friends will overlap (because people your friends know are people you also know and so on...) and there are many who won't bother to repost the link or are not interested in what you have to say. However, by posting to your friends, you are quite likely to get strangers seeing your link. If you have something a lot of people are interested in it could go viral and that means a hell of a lot of people see it.
I recently wrote an article for a blog page about ghosts. It was a simple article, giving my personal opinions on a ghost photo. It was not posted on my blog but on a blog about paranormal stuff. I posted a link to it on facebook. The owner of the blog posted it on his facebook. Not long after that, the stats for the blog showed over a thousand hits for that post alone (normal hits for that site are around a hundred or so per day). The link had gone viral and we were getting hits from all over the world.
We suspect, BTW, that the reason that article was so popular was because it was a 'cool picture' and absolutely nothing to do with the genius of my writing

And that is the key - find something to attract readers, make them want to come to you. Just posting the link may get some but if the content is not interesting (from the brief preview you get on facebook) many won't bother. Use a good title for your posts and good photos.
Many authors also use give aways and other treats to encourage likes. For example, they may set a target (if I get to 500 likes by this deadline...) and then say what they are going to do (...I will release an exclusive preview of my next novel... or, I will give a prize to the 500th liker or something...). This encourages people to post your links themselves in order to encourage them to like and therefore up that total to the target before the deadline. Be careful with this, however, as too much is likely to get you seen as a spammer...