How to build a community for an internal Q+A forum in a company?

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I setup a askbot site at my company a few weeks back, but the takeoff isn't as good as I had hoped.

Intially, there was some traction, as some people have been clamoring for a Q+A discussion forum for a while, but now there seems to be a chicken and egg problem- people don't check the site because there is not enough content, there's not enough content because people aren't going to the site and posting questions there.

The standard place to ask questions seems still to be in internal chat (ephemeral- no lasting documentation) or the internal wiki (long lasting- but doesn't afford good discussion) and occasional reply-all email threads on distribution lists.

For reference, we are a medium-sized software development shop. Have a few hundred people in engineering, who are the intended audience for this site.