Search everyones wallet in your house. Inspect the contents and take note of what is inside of each wallet. Then take a dollar and mark the top right corner the dollar with 3 small dots that only you can see using a red, green, and blue pen(or any other color). Place that dollar into your wallet and leave the wallet its usual place. When that dollar disapeers yo uwill want to quickly inspect everyone's wallet and search for that dollar. When you find it you will know who the thief is.
Alternatively you can go around confronting everyone with a bat and ducktape.