Here, we report that the introduction of silver seeds can lead to fast and high-yield syntheses of two highly anisotropic metal nanoparticles: triangular gold nanoprisms and ultrathin metal nanowires. Uniform sub-50 nm gold triangular nanoprisms were formed in high yields when silver seeds were introduced to the growth solution containing a small amount of silver ions and an aromatic surfactant, benzyldimethylhexadecylammonium chloride. On the other hand, gold seeds grew into spherical particles under the same condition. The formation of gold triangular nanoprisms from silver seeds was attributed to a relatively more reactive nature of silver seeds, which allows for the necessary structure evolution at the initial stage of nanoparticle growth. At high silver ion concentrations, ultrathin nanowires with the diameter of 1.6 nm were formed in nearly 100% yield. While both seeds (gold and silver) produced the same type of nanowires, silver seeds significantly facilitated the formation of nanowires, and the nanowire growth was almost instantaneous with silver seeds. We believe that the use of silver seeds in combination with aromatic surfactants can open up new possibilities for shape control of metal nanoparticles.