It may help to learn how you lost it. Such as, new computer, reinstalled Thunderbird, Attempted integration with other software, etc.

I meant to add: the file will have a prefix of abook@

I did an update and that's how they got lost

That can happen if you use an antivirus program, as many interfere with updates unless they are setup to avoid email interference. Since it was lost in an update, it may be in an older profile. You can investigate that by - clicking help>troubleshootinginformation - scroll down to 'profile folder' and click 'open profile' - exit thunderbird - you are now in the profile. If there is an abook.sqlite file showing, it is not up-to-date. - click the back arrow in WIndows file explorer to position yourself at the Profiles folder. - click that to see if there are multiple profiles (i.e., more than one) - if so, your missing addressbook may be there. All I can do is suggest comparing what any abook files are there with the files in your active profile. The abook setup may have multiple files with slight variations of the name. Together, they form the addressbook. If you locate a collection of files with abook prefix, you may have found your missing addresses. To save them,

 - first, in active profile (the one you started in), rename all abook files in case they are needed later
- copy all of the abook-prefixed files from the older profile to the active profile 

- restart thunderbird and check addressbook.