A few of my choices have already been listed. I've often thought Katy Perry would be a great tickler. Emma Stone would be a good one, too. As others have said, they'd be fun, playful ticklers, I think. However, for some reason, I am inclined to think that Katy might be a little more devious than Emma.
Back around 2006-2008, when threads on this forum asked for opinions on which female celebrities would make the most sadistic ticklers, Kelly Clarkson always made the list. I think she'd make a good tickler, but I've never seen anything about her that really screams "Sadistic tickler!" In my opinion, she'd be a little like Katy Perry--a little devious, but mostly playful. Plus, she has a sturdy build and some meat on her bones, so if she straddled my waist, I'd definitely be locked in to whatever she wanted to dish out.
I don't know if they count as celebrities (definitely not in a nationwide or worldwide sense), but there are a few news anchors that I sometimes fantasize about getting tickled by. One is
Carolyn Bruck. The other is
Katie Garner. Carolyn is an anchor at the local ABC station, and Katie is a traffic reporter. I'd cheerfully offer myself up to be tickle tortured by either one of them if the opportunity arose.