Try going to Settings>General>Restrictions and making sure the iTunes Store is turned on. If turned off, the iTunes icon will not appear on the home screen.
Search through your homescreens and folders, perhaps the icon is hidden somewhere.
Use Spotlight search to find it (a short swipe towards the bottom of the homescreen, to reveal it):
Usually this will find everything on your iPad.
In case it's impossible to find the app, backup and restore your device.