"Help" players cannot join my server!!!

If it is a firewall-problem you can see it in the log (run teeworlds in a console).

BTW: Please use the correct forum next time (Support).

I) have you registered your server at the master (heartbeat option)?

II) Have you ever heard about port forwarding? If not, search in the forum for a tutorial that covers this aspect. Somebody who I accidentally cannot remember has written a nice illustrated tutorial.

By the way, everywhere in the net, you will ingratiate with the community if you
a) can give the impression that you've used the search engine and checked the FAQ/sticky post (e.g. "I checked this (link) tutorial on firewall issues and couldn't find any aspect in that (link) FAQ)"
b) provide proper information on what went wrong and what you did on which Operation System (e.g. Windows? Linux? OSX?). [Yeah, you did at least the last part]
c) If you copy the information of the console into a textfile and upload this log on a hosting service and link to it, you are almost a pro in asking questions

Don't feel offended, I didn't intend to.