We use a technique called Structured Controversy in our large classrooms that I think would translate well online.
"Structured Controversy (SC) – sometimes referred to as ‘Co-operative Controversy’ or ‘Structured Academic Controversy’ – is a co-operative learning activity. During SC all students, working in teams and small groups during class time, engage in an informal debate like discussion about a controversial issue arguing one position in Round 1 and then another position in Round 2. The purpose of SC is not to defeat the other side, but rather to uncover the various arguments pertaining to the issue in question." - M. D'Eon 2009