When I do "required" discussions, I also use "ratings" such as 2 points for every post, up to 8 points max. I also read and rate discussions regularly, meaning that I am always participating. If I ever want to know which students have not yet posted, I simply go to the grade book, sort this grade book item, and look for anyone with no "grade." Of course, you can export the grade book to Excel for further analysis, if you wish.
This method can also be used to see if the instructor is participating.😉