Will Rogers Beach is a huge beach that spans most of Pacific Palisades. The beach's gay section is locally referred to as “Ginger Rogers Beach” -- near lifeguard tower 18 just north of the last buildings on PCH. I go there when visiting my LA friends. Fun scene.
In Santa Monica, too.....by a park called Dorothy Green with lots going on as lots of shops/restaurants alongside.
Nothern-ish Malibu also has more rugged landscape El Matador beach, which is gay nude, but often see thongers when I'm there. Not as much a populated scene.
If you make it down to Laguna, major gay beach with plenty of thongers is West Street Beach. Love it!