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)
The "Find my iPhone" app does not run on a computer - it is for iOS devices only, and only for finding another device from yours.
To locate your device, on a computer, go to http://www.icloud.com and log in. If the "Find my iPhone" service was setup on the device, it has power, internet and has not been wiped, you may be able to locate it.