Welcome to the Apple Community.
You can only locate your device when it is logged into iCloud and 'Find My Phone' is enabled, additionally the device will need to be switched on and connected to a wifi or cellular network.
Unfortunately, you cannot activate iCloud or 'Find My Phone' remotely.
If the device is wiped by you or another, you may not be able to locate the device (although some have reported they can)
Mister Winston Churchil, I lost my iPhone yesterday. Today a spezialist in a phoneshop could see, that my Phone is turned off. He could make out, that 'Find My Phone' is enabled. He said the finder will not be able to use the phone. The phone is keylocked. I was told that it is possible to locate the phone within 5m. I'm trying to find out how.