How to get my lost Xperia SL back even after factory reset? I'm new to this forum, I have lost my Xperia SL yesterday in a bus. I have registered police complaint with my IMEI number. I was trying to locate the phone using android device manager when someone uses my phone's internet. so far nothing is going correct.

When i log in to the google play with my email-id, my mobile phone model has been showing.

I have a doubt that, when the thief does a factory reset, and sign in using a new account in google play, will i able to still detect my phone with its registered model number? 
will i able to track my mobile with any of the technology? (I have not installed any tracking apps in my mobile).
or i have to wait for the police to track it with my imei number?

Can anyone help me to clear my doubts?

I have not changed my password of my gmail, so that i may have the more possibilites of tracking my device.
As soon as the device gets factory-reset, you can forget about tracking it with Google's Device Manager: As your Google Account on the device is gone then, there's no way for Google's DM to communicate with it.

Unless you've installed some anti-theft solution which integrates with the ROM (and thus survices a factory-reset – a feature offered e.g. by Cerberus, if your device is rooted), you will have lost all control then. But even a ROM-integrated solution would be gone as soon as a new ROM is flashed.

As long as it's still working, you could take a second device and follow the lost one. Once in range that you should be able to see it, you could trigger the 5-minutes-permanent-ringer. In the hope for an "honest finder", who should take this as a proof and hand your device back to you.

Don't wait too long, or the battery might be dead!