Use Find & Select, set Element Type to Object and add Criteria Library Part and set to Missing. You will need to go though all the Viewpoints as this does not work in the 3D Window.
You should add a Signature to your Profile (click the Profile button near the top of this page) with your ArchiCAD version and operating system (see mine for an example) for more accurate help in this forum.
Use the Attribute Manager.
Options>Element Attributes> Attribute Manager.
Activate the tab with the type of attribute you are seeking.
Select it and hit the Delete button. The program will ask you to confirm your actions before you can close the Attribute Manager
MacBook Pro Retina, 15-inch Yosemite 2.8 GHz Intel Core i7 16 GB 1600 MHz DDR3
Mac OSX 10.11.1
"Implementing Successful Building Information Modeling"
if you view the library loading report palette (the one you posted a screenshot of), and select the missing texture in that report, there is a blue button with 'i' to the right side. If you click that, a popup will show which surface is using the texture. You can delete the surface (assuming it is not being used) in the surfaces dialog. You can allways choose 'delete and replace' to replace it with some other surface.