Moved to Discourse Meta category.
If you click on a user, you should see their profile badge with a private message button. If you don't, let me know.
There's also private categories that only playtesters can see so you can post there to discuss things.
edit: you can see all the categories you have access to by going to the categories page. If you aren't in the playtests yet, there's definitely a chance you'll get in later.
These private categories will eventually be made public.