Sneaker Script.  Suggested by Lilly_Town 

I WANT THAT FONT TOO.. Anyone knows?

there is Another Katy perry font if you want it its not this but
its called Katy Berry

It's not a font because the two 'R's and 'Y's are different. The closest is Katy Berry.

Es de la familia Sneaker Script, pero la direfencia de las Y se debe al truqueo del photoshop