Sorry Micki, I new you called it a green coris wrasse, what I meant to ask was specifically what specie of fish it is.
The fish regularly (probably most often) referred to as "green coris wrasse" is Halichoeres chloropterus, if this is what you have they tend to stress easily and will disappear for days sometimes. Being moved & likely being put into water that differs from where it came from would be pretty stressful. I don't think that it would be too odd that it hid for a few days. I don't suggest digging through the tank looking for it, just adds more stress. After a week if you've not seen it, might be a thought to look for a body.
This fish is real good at (or bad I should say) jumping out of aquariums and getting into overflow boxes & filtration systems. I have found them on the floor when I have left the lid open and I have found them in O/F boxes and filter socks / pads numerous times in the shop. Even have found them is my sumps so maybe check your system to see if it is there.
Did you put it in your reef tank? If so, as it grows it may end up eating things you don't want it to. They get at least 6" long and seem to develop a taste for small hermit crabs & snails. They will eat peppermint shrimp and even smaller skunk cleaners too not to mention putting a big dent in your mysis population. That (mysis depletion) could become a problem for your mandarin. Mine also ate all my little feather dusters & tube worms. I did have a large pair of Banded Coral Shrimp that it never ate, I think they were just to big and mean for it to mess with.
Now to make things harder, C. venusta (males), Male Bird Wrasse (Gomphosus varius & Gomphosus caeruleus), Green Razorfish (Xyrichthys splendens) , Green Sea Dragon (Novaculichthys taeniourus) & the Seagrass Wrasse -- Novaculichthys macrolepidotus have all been sold to me under the name green wrasse or green coris wrasse at one time or another. Probably a good idea to determine exactly what specie you have so you can better know what to expect from it.
Joel