Lost device not showing on Find My iPhone

When you first set up the phone if you log into your Apple ID on the phone it will enable Find my iPhone (but it will ask you first). But you must log in to your Apple ID, because Find my iPhone is tied to your Apple ID.

When you go to https://icloud.com/find does it appear in the list of devices? If it doesn’t then Find my iPhone is not enabled on the phone. Did you receive a message saying the phone had been found, with a link to follow and log in? If so that was a scam to steal your Apple ID and password so the finder could turn off Find My.

You had to turn it on before the phone was lost. If you didn’t then it can’t work.

Does the device not show up at all, or does it appear as offline? Are you sure that you enabled Find My iPhone on it?

That means that Find my iPhone was not turned on.