For discussion, students who would like to speak can indicate this and each will be invited to speak, one by one. Students will be encouraged to be brief. For class participation: simply being "in class" almost all the time is sufficient to get a respectable class participation grade. Note that it isn't quantity of participation which matters the most; the quality of what you say is also being judged. We also make an effort give the floor to those students who have not had a chance to speak, at various times.
While students have a chance to add a post after the class timeslot has ended, this is not a competition to say as much as you can nor it is a task requiring lots of extra attention from you. Mention something if your "hand wasn't taken" or if you were unable to be online during the timeslot, make it brief and then move on to the other course requirements. The Piazza newsgroup will always be the spot for continued discussion of a lecture or an RPE.