Lost, deactivated phone being used by someone on wifi. Can I track it? The person who found my deactivated phone sent me a threatening E-mail from my own mailbox. He suggests he is has been reading my recent mail and says he found the phone in front of my house, suggesting he knows where I live. I have changed all my passwords so he won't get new mail but can access anything already downloaded.

Can I track this guy through the phone if he's using wifi or by IP address? He likely lives near me.
Yes you can if a) the phone is on
               b) wifi is on
               c) location is turned on (through settings)

As an experiment (using Android Device Manager through Google Dashboard) I tracked my phone with SIM card (cell towers) and with the card removed (WiFi). The wifi results were much more accurate.