1) Forget about it. We don't live in ancapistan, so you won't be able to hire a private investigator who will trace your phone and beat the thugs. Corporations and police however can do such things, usually you tell them device's IMEI and if thugs are not borderline braindead, the phone is long time powered off, flashed with IMEI-changing firmware if possible and smuggled to another country, usually poorer area where no one gives a fuck and police doesn't cooperate.
Do not forget to encrypt and backup your shit, that's the only thing you can hope for working 99% of the time.
Find-your-device only works in high social responsibility societies, if you accidentally forget your device in a cafe or hotel, they'll call your emergency number or bring it to police. If you forgot it somewhere else, you'll be able to find it via tracking software, this is where self-sufficient solution comes in handy. Write a script that sends encrypted coordinates and maybe a front camera photograph when you request it remotely via sms.
2) Data retention from telecoms, proprietary OS components, E-911, wire taps, SS7 vulnerabilities, IMSI catchers, targeted malware.
>>943736
>phones even know if you're a shut in
https://arxiv.org/abs/1612.03870
Current year Present day, Present time AHAHAHAHAHAH
I also know my city legally has access to such data which they use to plan transit system and streets "effectively". Individual businesses tack wifi clients inside and even send you text messages when they detect you walking nearby. Not even speaking of so-called "discount apps", that's pure data harvesting. Wouldn't ever touch that shit with a mile-ling pole.