Stolen iphone offline - tracking via icloud?

Hi
a colleagues iphone was stolen today and they've given me their icloud details to try help track their phone. Its offline so i'm assuming its been turned off.

if i check the 'notify when found' button will the thief know i've done this? I don't want to give them any idea that someone is trying to track them otherwise that phone is never going to be turned on.i'm also not doing 'lost mode' for that same reason.

also what is the play sound option?

Ok so if its offline either its out of network range or they restored the phone or off but play sound its when like your friends prank you and you play sound will make your iphone beep loud enough so that you can hear it. Some day thell have to turn the iphone on and no notify me thing will not let them know your tracking it.