Just some stats from Security Stack Exchange so you can get a feel for what might be right:

At the initial private beta we actually had 5 times more questions and answers per day than we do now, but this dipped to a fifth of where we currently are by a month of coming out of beta, and we were quite worried for a short while.

What we focused on then was ensuring good quality answers, monitoring tags SE-wide to check for questions which might be appropriate to migrate and most importantly of all, spreading the word:

 - twitter - especially around industry conferences - if a topic came up we'd ask a question on it, then tweet the link along with the conference hashtag
 - blog - post interesting questions or answers on our personal blogs
 - events - we let the SE staff know about key industry events and got sponsorship to some of them to attend, spread the word etc
 - numbers - we tried to get more of the community onto chat and meta so they could come up with ideas and help out (trying to do this with a handful of individuals is hard work)

As things came back up past the key thresholds, it spiralled up and became much easier to sustain and increase growth.

Try a bit of everything, and hopefully we can make this site successful.