The Apple App Store icon is one of the permanent applications on an iPhone or iPod, so if the app seems to be missing, it has likely just been misplaced. Here are a few methods that you can use to find your missing application.
App Store Icon is Missing
It may seem obvious, but the first thing that you should do to find your missing app is to do a full check of your device to ensure that the application has not merely been misplaced.
Double-check all application folders that you have created to see if the application has been moved. You can also do a Search on your device by swiping your finger to the right and typing App Store into your device's search field.
If you have set any restrictions on your device, this may cause an app to disappear from your home screen. To fix this, go to Settings > General > Restrictions, and enter your passcode.
On the next page, you'll see a list of icons with On and Off options next to them. Select the App Store icon, and turn it ON.