How do I make it visible?
iTunes 11.1.5 OSX 10.9.2
If you have enabled it, you should see it as shown on the screenshot.
Have you tried turning off internet radio and turning it back on via preferences?
Have you also tried quitting iTunes.app
and restarting it (with/without the preference selected)? I just tried, and it worked in all of these cases on my Mac (rMBP, OS X 10.9.2, iTunes 11.1.5(5) (64-bit).