Swipe down in the middle of the home screen, then enter the app's name in the search box. The app should show up in the Application results. If it's hiding in a folder that will be listed to the right of the app, and hopefully help you find the missing icon. You can also launch apps from here, if you want to.
If you still can find the app, then it's probably easiest to just delete re-instal it. At least in this case where you don't have to worry about losing any important data.
Go to Settings > General > Usage > Manage Storage (in the Storage section). Once the list appears, find your app, tap on it, then delete the app. You may have to tap on Show More at the bottom of the list if it's does not appear near the top.
Now go back to the App Store and re-install it.