Must the stolen money—taken as a percentage from the sale of a stolen device—be returned to its owner, or must the full amount be returned, and what is the way to do so if the owner cannot be reached?

The questioner's silence regarding his colleague's theft and then his taking a portion of the stolen phone's price are both reprehensible acts. He must repent and return the money he took to the phone's owner; if he is unable to do so, he must give it away as charity. He should also advise his thieving colleague to cooperate in returning the phone or donating its price.