Is it unethical for a boss to order employees to use their personal FB and Twitter accounts to promote events?

[Robert]

In my department we do promotional work for the company. Anyone who has a personal Facebook or Twitter account is pressed to use them to broadcast promotional events etc that we've been working on. I've been reluctant to join any social networking avenues, because if I did, I'd want to learn about them at my own pace, over time, like most everyone else has. And I'm a little afraid that if they got wind that I was connected, they'd take what I think should be a personal, happy experience and turn it into a JOB.
Am I wrong, or is it unethical to kind of force someone to use something they established in their PERSONAL life to do work activity. If you don't contribute, apparently you're regarded as a bit of a black sheep or a not-a-team-player.
Wouldn't it hurt your social networking presence on some level, too, making you look like a virtual walking advertisement?