If it still has some battery charge, or they plug it in somewhere, near some WiFi, you could set it to lost mode and include your email/phone number etc on the screen message.
They should be able to turn Airplane mode off from the lock screen without unlocking it.
Not much use this time, but for future reference - this old answer of mine is still worth considering - from Find my iPhone contact
Having a contact number actually embedded in the picture on your lockscreen makes getting in touch very simple, even to someone with little to no knowledge of how to operate the device.
