Two distinct Ag/Au nanocomposites, namely, hetero-oligomers and eccentric core/shells were obtained by one-step polymer self-assembly-based fabrication. The Ag concentration-dependent, facet-specific passivation, and presence or absence of anisotropic facets were the main factors responsible for controlling the structures of the final products. Based on an understanding of the role of Ag + ions in controlling the shape of anisotropic gold nanoparticles (AuNPs), tailored concentrations of Ag + were applied to design nanoparticles with desired anisotropic surface facets to allow site-specific Ag coatings on AuNPs. The Ag additives acted as shape-directing agents due to an underpotential deposition (UPD) that was responsible for stabilizing the various surface facets that enclose the AuNPs. The morphology differences between the substrate samples resulted in discrete plasmonic and sensing features. In surface-enhanced Raman spectroscopy (SERS) studies, we showed that the site-selective deposition of Ag on anisotropic gold nanohexagons (AuNHs) delivers more advantages as compared to their hetero-oligomer nanostructured counterparts due to synergistic effects.