More Servers at same computer

For each server use another port

For example 8303, 8304, 8305

You can start the server with many separate config files from the command line; Terminal in OS X.  Open your Macintosh HD, go to Applications and then Utilities.  The Terminal is there.

First, create a separate config file for each server, like Stephanator said, referring to a separate port for each server. All the servers can't talk on the same port, they'll get very confused.  Then, in the Terminal command line, type:

cd /[location of your server]/teeworlds_srv -f config1.cfg &

(& tells it you want to type more commands after the one you just entered)

Then, repeat the last line with config2.cfg, etc, etc.

For a sample, my username is Brad.  On my MacBook, I type:
/Brad/Desktop/teeworlds/teeworlds_srv -f bhop1.cfg & [Return / Enter]
/Brad/Desktop/teeworlds/teeworlds_srv -f bhop2.cfg &

You can also streamline this process by creating a script that will start all the servers at once.  I can go into further detail, if you'd like.

The alternative is to copy the Teeworlds server and libraries into separate folders, all with their own autoexec.cfg file, each referring to separate ports.  That will begin to eat up your hard drive space.

It´s only "sv_port 8301"