File a police report
Don't call 911, but do call local enforcement if your check book was in a vehicle or your home when stolen. In some large metropolitan areas, there may not be any investigaion of your reported theft, but you still need the police report number to help protect your interests.
Notify Your Bank
As soon as you become aware your check book has been stolen or lost, go to your bank and report the details including the check numbers in the book. This is important because the thief may use the actual stolen checks or order new checks with a different series of numbers.
Alert The Major Credit Bureaus
You should notify the credit bureaus that some of your personal information been stolen. Your checks may contain enough information to get credit in your name. You would have limited liability for any fraudulently obtained charges, but who needs the hassle. This is why you should not put your phone number, Social Security number, or driver's license number on your checks when you order them. Keep track of your credit bureau reports frequently. Each of the bureaus must give you a free report every year. Order them one at a time 4 months apart and repeat the cycle every year. That way you are getting the latest snapshot of your credit.
Alert the Check Verification Systems
Contact TeleCheck, Chex Systems, and any other verfying system in your area and report the theft. Many people only learn of fraudulent checks when their checks are rejected while standing in the check-out line.