Be sure to note the library where the item is located, the item's status (whether or not it's available to be checked out), and its call number.
If the item's status is Available, but you can't find it on the shelf, ask for help at the circulation desk of the library where the item is supposed to be located. If the person at the circulation desk isn't able to find the item, they will ask you for your contact information in order to submit a trace form. Library staff will then look for the item and let you know when it is found.
In the meantime, you might request the item via Interlibrary Loan (see How do I request an item via ILL?). Be sure to note in your request that the Library's copy of the item is missing.
Please let us know if you need additional assistance. We're happy to help.