Hi!
If you're talking about those talking on the main chat, then you can use the flag icon next to each post to send a flag report, and mods will get to those reports when they log online.
If you're talking about in pm, mods can be reached by finding someone online at that moment that has a mod on their friends list, then you would click the mod's profile and click the blue button "private" to message the mod you found.
For example; if a user named "applecat" was online and you clicked their profile to find me on their friends list you can send me a private message by clicking the private button on my profile and send me any screenshots you have of harassment.
You can either do this, or wait for a mod to log online. Even if the user is offline we can still kick them out and report for ban if necessary.
I hope this helped. ^^
-Ophelia