Engagement
I would argue that the best way to engage students is through the Socratic method. Indeed, students will certainly do the minimum if allowed. This is why, in order to engage them, I respond to their posts by using their name in my response, so that the student knows that I am speaking to them and not to the class as a whole. Additionally, I finish my post by asking a follow-up question that hopefully will prompt an ongoing conversation. Another trick that I often use is to email the student to let them know that I responded to their post and to hint that they ought to respond.
Scott
I often show the work of successful students I have had through the years. My students are very motivated when they see what a graduate is doing in the field!