Since attractive just refers to outer features, if you're interested only physically, that's fine. If you want a relationship, pick something that describes your person of choice better or encompasses more features.
"I think you're amazing, would you like to grab a coffee/dinner with me sometime?" would probably work.
If you choose to be this direct, make it clear you don't need an immediate response. The other party didn't have any time to prepare for this, so they may actually need to think about you in this way first of all. This may be the hardest part, because you will not know if you'll get a reply (depends on maturity and courage). You could ask them again once, but then I'd drop it and just assume it's a no, otherwise you may come across as pushy.
The reason most people don't do this is, that they're scared to be turned down or ridiculed (teenagers are assholes). I think from 30 onwards it gets a lot clearer and easier.
Good luck!
Cute used to describe a person? May work out in some cases, but in most it really will not for various reasons. She may feel you're infantilizing her, you don't find her appealing as a woman or appealing for the wrong reasons, you belittle her ...
As many wrote, used to describe her choices it's perfectly fine though.
If you're looking for a way to express how this person makes you feel - for example a continuous stream of "awwwww" may be expressed by calling someone cute - rather describe your feeling: "I could fawn over you all day." Ideally you also explain why, so it's clear where this is coming from: "The way you dress is a perfect compliment to your outgoing personality. I really enjoy just watching you exist."
Depending on who you want to be to this person and how far along on that road you are, my examples may work or be entirely out of question.