It isn't a surprise that wallflowers - is that the terms you kids still use - are a part of many gaming groups. Among the reasons people game escapist fantasy is a big one, and often the people who are quite shy in real life will play games to try and be one of those "people that actually matter." However, once things get going their natural tendency to hide and become reclusive wins out and they end up sitting at the table and perhaps only occasionally contributing.
Now, I don't want to make these people feel uncomfortable. But I did want to take a shot at doing a sort of collaborative advice column with this week's discussion. So, my discussion prompt for today is this: How would you draw a wallflower out of their corner and into the activity of the game?
The way I've seen work the best, at least short term, is to dedicate a small chunk of the game session to them. Even if they don't do anything super important, just give them the time to flex their character a bit and get used to talking and being the focal point. Let them pull back when they want, obviously, but give them that chance to try it out front and center. Later, when everyone is involved, make sure that you aren't ignoring them or missing out on them due to other activity. This can be hard, so it can be worth it to ask one of the more outgoing players to take the wallflower under their wing.
As a player if you want to help, one of the best things I've seen work is to attach your character to them. That way, even while they hide, you can have some quiet RP with them and help bring them out into the world while providing a shield should they get nervous.
How about you? What have you tried?