If there are cheaters in the server, say contact admin in normal chat. A form will pop up that you can fill out. If you select emergency, I will get a text message about the incident on my phone and can respond quickly.

You can also use this form outside of game:
http://www.sourceop.com/contactadmin.php

Make sure you select emergency, problem, or feedback.

Abuse of the form will get you permanently banned.