Historically, we've always seemed to have the same ratio (or even quantity) of active participants even on the old forum. What's great about today is it's no longer the same participants. It seems we have new names, more clients, and more non-technical participants and questions than just a few years ago.
Though I've seen active campaigning through Tweets, Meta posts like this, and personal emails work to increase participation, nothing seems as effective as showing someone how Tridion Stack Exchange works.
So I'm not alarmed since it'll always be a challenge for any community to encourage participation. Knowing a few of the participants personally, I would suggest our strongest fascination trigger are prestige, vice, and maybe power.
Consider ideas like:
- Tweets, contests, or other campaigns to answer unanswered questions
- Comments recognizing and thanking good behavior
- Poking fun of bad forum behavior (probably from other sites rather than this one, or doing so internally without embarrassing participants)
- Face-to-face and direct, friendly requests and reminders seem very effective
Once this participation becomes part of someone's online identity, then it's hard to make them stop participating. :-)