The best way to encourage collaboration between faculty and students is by enabling threaded discussion for wall posts.
This setting can be found within the class dashboard, under Customize > Look & Feel > Wall Posts
If enabled, users can create new threads (not just a single wall). Users can then post to those different threads and subscribe to receive emails whenever someone posts to it. You can also use it for questions and answers.
You can also manually approve wall posts if needed and allow students to vote posts up and down
For more information on this topic, check out this video