“I actually said that as a joke, but based on what iacisrmma said, it might be better if you don’t say why you’re calling.”
The Chofetz Chaim says that’s assur. You are only allowed to ask for and to listen to information l’toeles if the person knows it’s l’toeles. Otherwise, he is doing an aveira by telling you about the person since he is not speaking l’toeles, and you are doing an averia by asking him for information since you are leading him to sin.