I got an email saying I have a pending friend request, but I don't see one.

Please make sure that you received this request at an email address that is listed on your account. If the request was sent to a different email address then it will not show in your account.

In addition, if someone deactivates his or her account, you will not see the friend request on your Home page.

Feel free to send the other person a friend request from your account. Alternatively, you could ask them to request you as a friend again at the appropriate email address.