This is a guide about getting info on players, steamids previous names avatars etc. This will generally be helpful for reporting players so if you need to keep reading.
Steam Community Link : You can acquire this by clicking on their name in the tab menu in the server. After that there should be something resembling this at the bottom of the scoreboard.
You are going to want to click on the steam logo this will bring up their profile in the steam web browser using the steam overlay, at the top of the page will be a link which looks like this, or a bunch of random numbers if a player hasn't set their custom community link. The numbers are the player's Steam 64 ID, which is just an alternate to the normal Steam ID.
Highlight their profile link and copy it, you will then want to head to here
. Once there you should see this at the top left.
Paste the link with CTRL + V, and there you go