She wore her black hair ion a sleek swept over style with a side parting with a long low ponytail down her back.
A chunky silver and pink pendant and crimson lipstick added to her dramatic look.
The 26-year-old was supported by members of her family including mother Monica who wore a bright red frock.
Rhianna was excited about the bash, tweeting: 'Feel so lucky to have an evening like this, to spend with people with hearts like mine, who want to change and save lives at any cost!
She added: 'There's so much to do, and I can't do it all by myself, so I have to thank all of the supporters of and people who donated to #TheClaraLionelFoundation. 'Looking forward to seeing you later this evening.'And the singer got a good showing from her famous friends. But it may have been Rihanna's charity event, held in the extravagant Vineyard in Beverly Hills, but Kim Kardashian and mother Kris Jenner almost managed tosteal the spotlight from the singer, with there tacky wardrobe seen below.
Geometric: Tia Mowry-Hardrict looked striking in a one-shouldered black silky top and floor length skirt.
Hot mesh...Kim Kardashian and her Mom
All in one: Ellen Pompeo sported an eclectic all-in-one jumpsuit.