The right sign depends on your meaning.
Did you lose your keys or did you lose the game? Each uses a different sign.
LOSE or "lost" as in "I lost my keys."
Make the sign for "more" and then turn both hands palms down while relaxing your fingers. Pretend you were holding something between your hands and it slipped. This sign is used when you mean the opposite of found.
LOSE as in "fail a competition, or "We LOST at the track meet."
when signing "lose" as in losing a game, u have a "v" handshape go down to your palm. In the handshape's course, does it stop and turn a little or is the trail one straight line? The animation for "lose" makes it seem as if the handshape stops then goes very quickly.
American Sign Language University ™ ASL resources by Lifeprint.com © Dr. William Vicars