Overdue observations:
Find My iPhone needs an iCloud account, which some of us may decide to shy away from.
Find my iPhone needs data to work. As the phone is locked you cannot connect it to home WiFi. If you pull the SIM out - in case it is locked as default - you may not be able to restore the phone's data connectivity.
Email address on homescreen is something I do as well, the later Androids have that as a setup option.
The phone can be reset to factory default, only if it is signed out from iCloud (or never activated)
The best way seem to be
a) via Apple service centre, to get in touch with the Apple ID owner
b) via tel-Co service centre, to get in touch with the SIM owner.
The idea to call 911 is technically sound and quite cool, unfortunately little beyond ethical.