Tips for getting people to volunteer?

I have so many strong Bernie supporters on my FB friends group and I've been messaging and messaging and messaging to try to get them to help out. I've gotten one (my best friend) to start phonebanking and we went canvassing for the first time today. But nothing from anyone else.

I can't pretend to be on some high horse because I've only been phonebanking for a little under 2 weeks and just started canvassing today, but I just find it frustrating to get my friends to understand that THEY CAN HELP. They all click "like" on my posts calling for volunteers but there seems to be little effect. It's especially frustrating because a few of them are like 10 times more outgoing and congenial than me and would do so good at phonebanking!

What can I do to motivate them without coming across as nagging or preachy?