Group chats can get confusing, especially if you've got a bunch of big talkers in the thread. If you need to get someone's attention in Hangouts, there's a handy little trick for doing it. Just long-press on the user's avatar and you get an @name reply.
This will work with the profile image next to any message that person has sent in the thread previously. It won't specifically alert that person any differently than a regular message, but the name should make it clear you're talking to them in particular, and not the entire room.
We checked it out, and this seems to work fine with regular Hangouts conversations and group SMS in the Hangouts app. Now go forth and reply.
[Thanks, Paarth Desai]