Is the app still installed on you Nexus? To find out, tap on the icon at the very bottom of the screen with the circle containing six small dots, that will bring up a screen showing icons of all of the apps installed on your Nexus. You may need to swipe a page or two to see all the apps. If the TuneIn app icon shows up there, simply press down on that icon for a few seconds, that will copy the icon onto the home screen.
Once in a while an icon vanishes from the home screen on my Nexus, no idea why, maybe I inadvertently erase it. No biggie, it's easy enough to restore.
If it's not that, then sorry, I got nothing.