Social networking enables a tremendous range of communications methods. But if you really want people to do something, there is no substitute for a phone call or in-person visit. A vast amount of my time these days is spent on the phone. And, where possible, on a fixed land line, where I can get good voice quality.
My main non-work-related endeavor these days, for anyone who hasn't caught on, is putting together a party to run for local elections (mayor & city council) in my town, Hod Hasharon. For those purposes, sending out e-mail really sucks. It simply is not possible to get people to physically show up if you send an e-invitation (unless you are really a rockstar). It is not possible to get people to volunteer their time, even for something in their own interest, such as their kids' school council, unless you pick up the phone and talk to them personally.
To get someone to do something, you need to understand their capabilities, their motivation, but moreover -- you need them to believe you understand them. You need them to believe this is going to be a success. You will never achieve this by e-mail. You can't listen to someone by e-mail. You can do it by chat, with certain people under certain circumstances. But for most people, it must be by voice.
E-mail is tempting. At this point, my group is too big for me to be able to call everyone every week. So I use e-mail to update people. But mostly, I have to talk to them. There is no other way to truly motivate.