The Heroes of Olympus question

I have read the Percy Jackson serie, and I LOVED it. I'm going to read *Heroes of Olympus* next, but I need to know how much we see of Percy in the books. I know that he is not in the first book *The Lost Hero* he is only mentioned.
I know that he is a main character, but how big of a main character are we talking? I don't want spoilers, but I just need to know this before I read the books.
Hope you can/will help me.