Is it outside or in a pot?

I'd echo Owdboggy's response and add some more queries - in full sun? How long have you had the plant?

Is it in a windy spot? Acers hate wind.

So you water it, and it still wilts? We definitely need more information: has it been repotted recently? What kind of soil is it in? Have you added soil on top of the original soil level?
Lack of food will cause new growth to stop, and older leaves to turn yellowish, but won't cause wilting. On the other hand, Acers in tubs do need feeding on a regular basis, and prefer an ericaceous plant food.