Various defect sites on SiO2 thin films on Mo(112) have been characterized with metastable impact electron spectroscopy (MIES), and the interaction between deposited Ag and these defects sites investigated with MIES/ultraviolet photoelectron spectroscopy (UPS). MIES/UPS data for low- and high-defect SiO2 surfaces acquired as a function of Ag exposure are consistent with two-dimensional Ag growth at low coverage and three-dimensional growth at higher Ag coverages. With increasing defect density on the SiO2 surfaces, no significant change is observed in the behavior of the work function with respect to the Ag coverage, suggesting that the interaction between Ag and SiO2 is not influenced markedly by the presence of defects. This result is consistent with recent theoretical results that indicate a strong covalent bond between an overlayer metal and defect sites of SiO2.