Solution 1 - ps

Run

ps -ax | grep node

You will get something like

60778 ??         0:00.62 /usr/local/bin/node app.js

Then do:

kill -9 60778

Solution 2 - netstat

Instead, do this:

netstat -punta | grep <port>

If the port is being held you'll see something like this:

tcp           0      0.0.0.0:<port>          0.0.0.*       LISTEN     <pid>/<parent>

Now kill by pid

kill -9 <pid>