If your iphone 6 plus is connected to Wi-Fi (the phone is not on service ) can you still use find my iphone

:}

TRY IT AND YOU KNOW!

Yes you can still use Find my iPhone.

In reality, all it needs is an Internet connection; either Wi-Fi or mobile data.

Of course, if the phone goes out of range of the wireless network, FMI won't work.

Yes. It just needs internet, be it Wi-Fi or data. Of course just using Wi-Fi would severely limit its ability to work (or be helpful)