Hello  Mi user,
if the device is logged and if you want to track the device there are three condition If all the three are ohk then you will be able to track the device
1. Device should be logged in with an Mi account or Gmail Id
2. In Setting Mi account there is an option for Mi cloud is there and in Mi cloud enable Find my device option.
3. Internet connection of the device should be on.(for working GPS internet is necessary)
If ll the 3 condition are ohk then you can log in to I.mi.com and you will get an option like find my device and tap on that it will show the approx. location.
If its not  then you have to visit to police station with invoice copy and raise a complaint from there they will try to track the device with IMEI number.

Note: Why company is asking to login with an Mi account is in case if you lost the phone who ever is taking the phone he will not be able to use the phone even if he do a factory data reset or fast reboot then also he will get a pop like the device is logged in with mi account enter password and he will not be able to do that. And if he use a different number on the device without doing a reboot you will get a message on your registered number that the device is having this sim number.

Thanks with regards