If you run a message board community, the lively chatter between members is one of the things that makes the site work. If people don't talk on your site, it won't last long. You can't keep an eye on your forum and answer every post, but as an administrator, there are a few things you can do to get things moving again.
Set up a contest. Yes, because who doesn't like to win something? You don't have to spend a lot of money, and the winner's prize can be as simple as a subscription to a magazine, a free membership to your site for a year, or an electronic gift card. Want to make it big? Find a business that will pay for a gift, and in exchange, give them free advertising on your site for a set amount of time.
Update your icons.
The same old, boring icons will definitely make you want to yawn. Switch out one set of icons for another to make things more interesting. People like icons with holiday themes.
Change your theme or background.
Holiday-themed backgrounds that make people feel warm and fuzzy will keep people coming back to your site like nothing else. Put away the boring, sterile backgrounds and give your forums some holiday cheer.
Cyber Grab Bag.
I haven't tried this one yet, so no. But I do know of sites where people play "Secret Santa" with other people who are also members. This can be done with a surprise email, an electronic gift, or a donation to a charity that the person likes.
There are a lot of other ways to get your site back up and running. Use the holiday season to come up with a plan that will get people interested in your website. If you're not sure what to do next, ask your members—they'll know what to do!