A roommate once stole my checks and forged them. This should be fairly easy to track, actually. Most banks have video monitors. You go to your company, explain what happened, and ask for the specific check #/security code. Then go to the police, and they'll try to track the check. Most banks require ID's, so you might want to make sure that this isn't a relative or someone who looks passably like you doing the stealing. Then go to your company and ask them for a cash advance, or go to your landlord and explain the situation.
And obviously, get direct deposit and be more careful next time.