You should have posted this in the Mod Implementation forum, as this forum is only for the base version of Snitz (currently 3.4).
Log in to the admin section and choose Config Active Users. Look for Allow Active Users Panel under Active Users Panel Options and set it to the choice you want. From your question, I guess that is currently set on Feature Off.
Active users isn't a feature in a standard version of Snitz, it's a modification which you have to add manually. You can find the download link in the first post of the topic below and a couple of bug-fixes in it as well.