Both are Social Networking websites but I think there is only one difference in both websites. In Facebook we can advertise our website whereas there is no option for Google Plus.
Google and facebook are worlds largest social networking websites. With google we can search for information and with facebook we can share our photos and do chat.
Both are Social Networking websites but I think there is two major difference b/w Google+ & Facebook is:
Google+ = Provide do follow links / Facebook = no follow links
Facebook = We can advertise our website / Google+ = there is no option for advertise
One important difference Google Index the links and you can get #1 with a post if you have some good circles, with Facebook no.
Slowly Facebook loses from it's authority. Personal opinion. Before when FB links were indexed a lot of campaigns were going there, now they are not so effective. Google is smart. So, even though Facebook has like 500 million users is not comparing with the results you can get from their services!