How to find your iPhone when you don't have the find my iPhone app installed?

How do you find your iPhone when you don't have the find my iPhone app installed?

Added (1). If you have iCloud on your mac can you do it from there?

You don't.

Call your phone from your moms cell phone or your house phone and you will hear it ring

You don't, if you were too lazy to activate it then do without it.

How can you find it if someone stole it and you know who it might be but you don't know what should i do