I think as suggested a few posts above, you could provide the time interval of members to sign up to create their threads. For example, let's say that tomorrow, you could allow about, I dunno, 5-10 people to sign up to create threads, and those threads can be approved, while the rest ask questions, or whatever. The people who signed up could wait a couple of weeks before posting one again, or maybe there can be a general wait list for people to create threads?
Whichever the case can be, maybe by having a smaller number of threads at one time, there can be more encouragements for people to ask questions to members that they don't know or don't speak to on a regular basis.. I mean, of course, it's ultimately the members' decisions and initiatives to ask questions to the people that interest them, but you know, even the smallest encouragements can help?