Facebook, LinkedIn, Twitter, Google+, YouTube…there are so many different social networks that it might be tough to decide which is best for professional networking. I tend to believe that networking happens best face to face instead of online. I've only been teaching for six years and have only had two jobs, but both of them have been connected to people who I didn't know directly, but someone close to me knew. Networking, to me, has deeper significance when it happens in person. If someone were to say to me, "I know someone who could be a guest speaker in your PE class," I would be a lot less inclined to invite them to come than I would be if I actually met the person and was then told, "This person can be a guest speaker in your class."
If I were to choose an online networking site to represent me professionally, I would definitely choose LinkedIn. I think that Facebook and Twitter are too informal and social, and shows some pointless information when it comes to being professional (for example, saying what kind of TV shows or books I like). I'm not super familiar with Google+, and I don't post videos on YouTube at all, much less related to my profession. LinkedIn, on the other hand, is set up with the intention of networking professionally, so it automatically eliminates some of the possible distractions that other sites offer.