Twitter is for looking at what people are doing and telling people what you're doing and trying to feel important. Facebook is for interacting and looking at pictures. Google+ is google's attempt at killing Facebook and getting your personal information.
And Facebook is getting your personal information’s too and they give it to CIA and other authority’s not only Google+ is doing that but the most of popular social networks are taking information’s
Facebook: Stay in touch with friends and family Twitter: Follow and share your interests with the world Google+: Stay in touch, follow and share with friends, family and the world
Facebook focuses on connections - keeping in touch with your new friends or your old acquaintances. It's nice to get an update of your friends' lives every once in a while. Twitter focuses on interactions - starting a public or private conversation with somebody else over a common interest and topic. You're even encouraged to converse with complete strangers on the Internet, as opposed to just the people you know. Google+ focuses on a little bit of both, but on a smaller and more private scale. It helps you interact with your friends without broadcasting your conversations to the world.
You've forgot about LinkedIn which is focused on business connections. Nevertheless, Facebook is also important for business connections. At both FB and Google+ you can launch brand pages. With active work there you can get much traffic to your website. Google+ is not so popular now, but it's important as it gives some bonuses to your ranking in google.