According to Percy Jackson himself, Logan Lerman, speaking to MTV says:
"It's not happening. It's been a great experience for me. It's opened up a lot of doors for me, but I don't think it's happening."
But goes on to tell The Independent: that he is contractually obligated to do a third film if it does go ahead:
"I just haven't heard anything about a third film. Unless they call me I think it's unlikely".
With a budget of $95 million, Percy Jackson and the Lightning Thief made $225 million while Percy Jackson: Sea Of Monsters made $200 million from a $90 million budget.