If you cannot see anything obvious then it could be slugs or caterpillar damage, more likely slugs. Shriveling up of leaves is a sign of stress - too little water, too much or a reaction to insect attack. You can deter slugs with broken egg shell and copper rings around the base of the Acer.

If the holes are very small, and some of them look like tiny indentations rather than actual holes, it could be capsid bug. You don't usually see the blasted things, just the damage they cause. Use an appropriate pesticide which treats for them.