Directly after Charlie went to tend to Penny, Percy stood in the midst of the party and looked around; Charlie was gone, and so was Ginny and Harry. Angelina was here, too, wasn't she? She wasn't to be found, either. They would have to be told individually, later.
Adjusting his glasses and taking on a mode that was reminiscent of his days as Head Boy, Percy spoke loudly, "Attention everybody! It would seem some prankster has spiked the Cauldron Cakes with a strong love potion that has immediate aphrodisiac effects." Of course, Percy spoke from personal experience. "I suggest we steer clear of them, lest an embarrassing and potentially damaging event occur."
The prankster that Percy immediately had in mind was his brother, George, who was notorious for these sorts of things. As sensitive as he was about pranks and his brother, he wondered if George was trying to directly get after him. He'd already experienced the cupcake's effects earlier this afternoon - did George go so far as to taint a supply of Ministry's cupcakes, as well? He wouldn't put it past George.