Looking for opinions on author platforms...

All us aspiring authors know that if we are to be successful we need to build a social platform. Every book or article on becoming a successful writer tells us this. Yet when we go out to create one there are almost too many options. I have a Blogger account and that's about it. I have personal Facebook and Twitter accounts, but I don't want to use those for networking because most people in my real life don't know that I write so seriously.

I'm starting to think I should set up writing accounts on Twitter and Facebook. But then there's Wordpress, Tumblr and personal websites. My question is, just how many of these things are necessary when you're still at the 'aspiring' stage? What tools do you all use?