iTunes Store app disappeared from my App Library on iPhone

I just noticed that my iTunes app disappeared and is not in my App Library … I used it yesterday, so I know it just happened, but Why!? And how do I get it back … it doesn’t appear in an App Store search. I’m panicking a little because I love that app & I use it a lot — it’s comprehensive and easy to use! Any ideas, updates, or fixes??

[Re-Titled by Moderator]