How to require passcode to turn off iPhone

I dont understand your question. Do you want to set up a passcode for your iPhone or you wanna enable find my iPhone on your device?

Vtx89asp wrote:

in order to avoid iPhone to be turned off due to a robbery or loss I need to require passcode for turning it off so i can find it through find my iPhone app

For lots of very good reasons, that's not an option. If you search the forums, you can find a number of discussions on the issue.

Submit your feedback directly to Apple using the appropriate link on the Feedback page:

http://www.apple.com/feedback

You can't...at least not yet. No one knows what Apple could add in future updates.