De-lurking is a myth.
It's a tempting myth (f you could just get 5% of your lurkers to become active, the level of activity would skyrocket!), but still a myth.
It's not going to happen. Your lurkers aren't going to become regulars. This isn't ouropinion, there are great studies too.
I'm sure you can find a few anecdotal examples of long-term lurkers that became regulars. These are the exceptions, not the rule.
Members don't read, browse all the available topics, and then decide to participate. They make that decision very quickly. Review the stats in your community for yourself.
Lurking is the result of two things. 1) A lack of engagement initially and 2) The member's level of interest in the topic.
The time and effort trying to engage lurkers is better spent trying to engage your newcomers. If you get this right, the level of activity in your community will skyrocket.
p.s. Our December edition of community best practices is out. Click here to download it.