Leo already knew Percy was gone. It was hard not to notice the lack of an extra person around the house. Or the fact that Annabeth had been depressed about it. So when he saw her make a post on the network, he left to go find her.

Once he does spot her, he sits down next to her quietly and gives her a gentle nudge, but doesn't say anything. What is there to say? Sorry your boyfriend is gone just doesn't seem to cut it.