This post by Lorianne DiSabato ("It's time to teach human, again") suggests that online conversations - specifically asynchronous threaded discussions - can help more introverted people contribute to discussions:
In my face-to-face classes, I notice with regret how students’ personalities sometimes hinder their academic performance. There are always a few extroverted students who dominate discussions, for instance, while their more introverted but equally intelligent peers are less eager to participate. In an online class, however, no one can sit in the proverbial back of the room where an instructor might overlook them. In an online class, everyone participates, and everyone has a chance to think before they contribute. In an asynchronous threaded discussion, you can easily refer to something a student posted earlier in the week and connect that comment to something another student said today. In an online class, all students’ contributions are recorded regardless of how outgoing they are in person.