How to track a lost or stolen iPhone without iCloud information?

"Lost phone: My son’s phone is lost or stolen. He can’t remember his iCloud information. We can’t track his phone on Find My because his phone is not on my list of devices "

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Recovering an Apple Account:

This all comes down to account recovery. If he forgot his Apple Account info, then it seems he need to reset the password. The eMail address he uses for his Apple account is his Apple ID. As for the password, if he cannot get it, perform a reset. Use a Computer for this, as it would be more user-friendly doing so: If you Forgot your Apple Account Password - Apple Support

Finding the Device:

Troubleshooting a Lost iPhone

Alternatively to using Find My, you'l have to do so the old fashioned way. Find My can only be enabled directly on the iPhone. It cannot be enabled elsewhere. So, is it enabled on the iPhone?

So, what to Try:

• Dial it: See if it is heard ringing

• Ask Local Authorities: See if it has be hanged over.

• Text It: Ask whomever has come across it, to contact you.

• Ask Someone: See if someone you know (i.e. Friend, or Family Member) if that came across it.

• Backtrack your Locations: If you are at a coffee shop, or a library, stop by and see if it was safely placed aside.