I know that bounced checks can bite me in the ass later, but I have no idea whether any of the checks were actually taken out of my checkbook. I thought about looking at my bank account, but I visit my therapist every 2 weeks or so and pay my copay with a check, which usually takes her a little while to deposit, so I'm not sure I can rely on account activity to determine what check I was on before the checkbook was lost. (I know that's a bit convoluted-- hopefully it makes sense!)
Get a list of transactions from the bank.
Then with people you know you've sent checks out to, ask if they deposited the check yet.
If they have, you know that anything that isn't on the bank register and isn't still in your checkbook is missing.
If they haven't, ask them the check number and use that as the last check you wrote.
Once you find the last check you wrote, if you have any missing checks, ask the bank to cancel/watch/flag any missing check numbers. Maybe they can catch the person who is using your checks.
The purpose of a check register is to record checks written. If you have it and the checks were returned to you, it should be very easy to determine if there are any checks missing.
If the checks had not been returned, I would have immediately spoken with the bank to determine the best way to manage the problem.