I've already posted an answer to this question on the last thread you posted it on (I have stolen my iphone6 . I think find my phone is off. Is it available to know location when the phone is turn off?):
If the person knows your Lock Screen passcode, then putting it into Lost Mode isn't going to help. If you have your phone backed up to iTunes or iCloud, your best bet would be to erase the device. If you have Find My iPhone turned on, the thief will not be able to do anything with the device once you have erased it. Erasing the device does not turn off Find My iPhone. It just removes your personal data, and renders the device useless to anyone who has it.
Best of luck,
GB