If you remove the Passcode on a iPhone 4 will the Find My iPhone app still work?

I lost my iPhone 4 on Saturday & I switched of the cellular data before I lost it & the Phone has a Passcode, Can the Person who stole my phone unlock the Phone in Namibia & will I still be able to locate if he removes the Passcode. I don't have the serial # My dad brought it from Germany without a box. & I tried Locating & Locking it but its currently offline

Impossible.

If he want to use your iPhone but can't unlock your Passcode, he will connect to PC and reset your phone.

Find my iphone only works with All these conditions.
1. Power ON
2. Find my iPhone is enabling.
3. Internet connection(cellular data or Wi-Fi)

In fact, he will reset and format your phone when he can't use it.
Or,
He unlock your passcode, but NO internet connection is available. You can't locate it.

Sorry to hear that, guys!

Btw, my mother lost her iPhone several days ago… We're failed to find it back…