The former Bond Girl adopted a baby girl called Eloise Joni Richards in June. She also has two daughters with ex-husband Charlie Sheen.
Richards revealed on her Twitter account that the theme for the weekend celebration was "three is a charm".
She later wrote: "Thank u my amazing friends for celebrating my baby daughter yesterday... I love you all and feel so blessed to have you in our lives....xo (sic)"
Tori Spelling, Lisa Rinna, Ali Landry, Nancy O'Dell and Ali Sweeney were among those on the guest list for the celebration at the Montage Hotel in LA, according to People.
Among the gifts received by Richards was a three-tier white and pink cake featuring small figurines of the star's daughters Sam, Lola and Eloise on the top and the message 'We love Eloise' written on icing on the side.
Richards previously told Us Weekly that Eloise had "brought so much joy" to her family, saying: "She loves being hugged and held. She's such a beautiful little baby and little soul."
The new arrival was named after Richards's own mother Joni, who lost her battle with cancer in 2007.