You cannot anymore in the new forum.
Check their profile or post it in the job section.
You can also reference a user to get their attention and they might give you a way to contact them. Like this:
If you check their profile you might see them in social media or similar.
For example if you check my profile you can see how to contact me on Facebook and Twitter or find me on YouTube or Patreon.
I hope this will help.
Feel free to contact me as well if you cannot get their help to help you in develop the game.