Looking for a script " like us on facebook and get item free "


 I got this website and server and i am looking for a script / app , something like :

" Like us on facebook and get a ( item name ) free "
If anyone can help me in this matter i would apreciate it. Also i want to let you know that i don’t know anything about this matter.
So! If anyone know something, please share it with me.

Thank you!