i managed to track my stolen iphone but i want to catch the thief too.

Location services can be turned off, but that does affect Find My phone. Their only option is to keep the phone powered off to thwart you. When you send the PLAY SOUND (plays at full volume even if the volume is all the way down) command or the ERASE PHONE command, they are received by your phone (regardless of location services) as soon as the device is turned on. You can annoy them I guess.

for what it's worth...

A man was shot to death near here earlier in the year for chasing his stolen iPhone. He tracked the device down to a car at 3am and when he approached it, they shot him.

For a phone.

To answer your questions... they would have no way of knowing you are tracking them. Lost mode is likely not going to turn them into nice people. They can't get your data or re-use your phone. When they turn it on, they can't disable location services or turn off find-my-phone without your Apple ID & password. The phone is totally worthless to them, unless they can get a greedy simpleton to give them $100 bucks, no questions asked. By the time the buyer realizes he can't use the phone either, the thieves are looking for another phone.

The Find My Phone option is not a great way to get phones back. It is much more effective for lost phones.

The belief is that by reducing the value of a stolen phone that can't be re-used *should* make them less desirable. Sadly, there is one born every minute and people keep buying them, believing there is a way to get past the activation lock. There really isn't.

The main upside for phones is that your data is safe. Gone but safe. That's assuming you have a backup and can restore your new device from it.

Contact the police