I agree with Mary that a think-pair-share works well to involve more. I always use a community circle first when I ask for a reflection. I have never had a circle where "everyone" passed! That includes a few more as swell but of course is time consuming. I really like the strategy the "Final Four" as well. I post what four reflections I need before we move on… or out… and it isn't long until everyone clues in that we are going to get those four before we move on. By adding the good clean funny joke each time there is always a good laugh to end the session as well. When I do these types of activities to involve more students, I always remind everyone that out of "mutual respect" we need to hear lots of ideas presented so we will… do a community circle or a final four or two for Tuesday etc.
Try using "think-pair-share", a Kagan cooperative learning strategy that works well for a quick reflection. Student turn to a partner and share the answer to a question, a reflective thought, or simply paraphrase some information. Then you might have students share "what you heard from your partner" to encourage attentive listening as well. Another strategy is the "ticket out", where students write the answer, a reflection, a statement…on a slip of paper and the teacher collects at the door. If students are required to sign name to their slips of paper, there is certainly more accountability.
I have one student who ALWAYS has a great answer for my reflection questions, but she is usually the only one to answer – what do you suggest to get the other students involved?