Wrasses are like that. Provided there is no crab or other devil-like critter in there, it is very common for wrasses to disappear for even a week when first introduced. They just hide...even if you look for them everywhere. Wrasses are very emotional...
When I put my 3 McCosker's Wrasses in the reef I didn't see any of them for about 6 days, then I saw one, and an hour later they were all out swimming about like nothing happened. When I added the Yellow Coris Wrasse he hid for 3 days. Some wrasses hide in the sand, some hide in the rocks.