Response to group work

I have been having a similar problem with class discussion. I ask a question or ask them to comment on whatever the reading was, and it's relation to our discussion in the previous class, and basically get cryptic answers followed by a great deal of silence.

I have set up a blog for them to begin to discuss the readings online, with two discussion leaders assigned per week that are expected to get the conversation going. I figured it would start slow, but expected this environment to be a bit more relaxed because they would have time to think about their responses and edit them, instead of doing it on the fly in class. However, their responses on the blog are similar to those in class, not a great deal of interaction, basically just 7 separate comments.

I like the idea of group work, but with 7 students, I already feel like we are in a smaller group, and worry that having three or four in  a group would not be enough to get them to open up.  

I have been considering introducing some of the basic terms in fiction and poetry through a version of Balderdash, just to get them thinking about these terms in a creative way, while addressing the different ways we can use these terms to talk about the different stories and poems we are reading. In the end, I really am just forcing them to interact with each other, but I am also hoping that this sort of interaction, in a more relaxed environment, would help them get over the jitters of speaking to each other in class. What do ya'll think about that? Am I setting myself up for disaster, or is there possibility here?