How do I get my girlfriend to be more ticklish?

I'm dating this great girl right now with a really hot body. We always have a great time together and are having great . The only problem is, she's just not ticklish enough for me. All the girls I've dated in the past were very ticklish all over their bodies and would laugh like crazy when I held them down and went for their tummies or their feet. It was always a lead up to and a way of being intimate. I just don't feel that same degree of intimacy with this girl since I can't bring the same laughter out of her. She just smiles and closes her eyes when I try it on her. Does she have ticklish spots that I'm missing? And how can I find them?