Log out and look for another user account, if all you did was install Mavericks it would leave all of your data alone. However if you did an erase and install then all your data is gone. Either way you can simply restore from Time Machine or a bootable clone.
You may have logged in as a different user, such as Guest. Open the Users & Groups pane in System Preferences. Your name should be at the top of the user list, under Current User. See also this support article.
If files are missing from one folder
Change the Finder view mode; for example, from icon view to list view, or vice versa.