My stolen iphone SE doesn't have a passcode lock or a sim card, how to I render it useless?

My iphone doesn't have a passcode lock or a sim card, it got stolen, how to I render it useless to the thief? It's currently in ios10 , it's still listed on 'My Devices' on my apple account so I can still see the Imei number. How do I render it useless? it doesn't go online on FindMyiPhone and the theif has most probably factory resetted it.