$ sudo killall nginx
Password:
No matching processes were found

When I try to run it, the same error occurs.

To uninstall it, since there was no "easy" way to remove it, I just removed every file or folder which contained any nginx in its title or anywhere in the contents. There didn't seem to be any other way to remove it.

The first time I installed it, I did a manual install. The second time I used: "sudo port install nginx".