You might try
lsof -i
To see which process/pid has port 3000 open. It will show up as something like:
ruby 94580 7u IPv4 0x08681274 0t0 TCP *:hbci (LISTEN)
The 94580 is the PID. The hbci is because port 3000 is used for that protocol (apparently).
On linux netstat -nap would show which processes have which ports open. Sadly -p/-o does not seem to exist on the mac version of netstat.