NFL Stars -- THONG HUNTIN' ... On Australia Beach

SF 49ers star Patrick Willis knows what he likes ... CHICKS IN THONGS ... and he went after it hard on a beach vacation to Australia.

Willis -- along with former NFL linebackers Takeo Spikes and Carlos Emmons -- are on a boys trip Down Under and decided to go searchin' for ass on Bondi Beach.

Good news -- they found it.

While Willis was able to pull off the 2-on-1 all by himself, Spikes and Emmons teamed up to chat up two other thong'd up ladies who were catchin' some rays.