According to their facebook page, they are now testing block list.
The last 3 players you’ve thumbs-downed will not be put on the same team as you unless your wait time is too long; this will only affect thumbs-downed teammates
So all my life have been a lie. I thumb down trolls and afk, and they are still got matched with me again in my team. Thumb down has been just a way for you to release your anger, since we don’t have the question mark ping anymore.
JK I know deeply that Thumb Down does not do anything. I mean who care about Karma anymore right? It’s funny how now they make a official statement about it. Full of lies.