You can’t do too much about the number of lurkers in a community. You might be able to shift the metric (participants / registered visitors) by a percentage point or two, but this comes at a crippling opportunity cost.
And that opportunity cost is to capture your current visitors.
You should worry far less about lurkers and far more about visitors who never come back to your community at all.
When you build up a detailed profile of your visitors (the people that visit but don’t register), you will notice that the majority of these visitors were entirely satisfied with their community experience.
They visited, received an answer to their question, maybe browsed a few other pages, and left.
If they have another question, they will visit again. But that’s not very likely.
You will also notice that they are open to being surprised. If you can give them useful tips they can use, highlight some people to follow on Twitter about the topic, or prompt them to sign up for a relevant webinar, they would be interested. But it has to be really relevant to their situation.
This is really hard to do in most communities as it involves either manually going through your most popular discussions and adding/updating links or tweaking the technology to enable pop-ups or other notifications of something surprising.
But the opportunity is there. It’s a big opportunity. Most visitors leave your community entirely satisfied. What if you can keep them there and engage them in something exciting?
p.s. Podcast interview on all things entrepreneurship.