I'm glad to be able to tell you that even if you've never installed or used the Find My iPhone app (Download at iTunes), you still may be able to use the service to track your phone. This is possible because the Find My iPhone app isn't what makes your iPhone trackable.
Find My iPhone is a cloud-based service offered by Apple. This means the service lives on the Internet and is accessible over the Internet. The Find My iPhone app is one way to use the service, but you can also use it in virtually any modern web browser by just going to iCloud.com and logging in with your Apple ID.
So, just like your web browser, the app is just a way to use Find My iPhone, it's not the service itself.
Enabling Find My iPhone on your phone is something that can be done even if you never install the app. If you've turned on iCloud on your device, there's a good chance that Find My iPhone was enabled. If that's the case, you're in luck--your device may be trackable.
The Find My iPhone app is really designed as a way to track your lost or stolen iPhone. You can do that tracking on a computer, too, but if you're trying to hunt down your device on the go, doing it from a phone is usually easier when you're using a laptop.
Last Updated: June 12, 2013