Chris Brown parties with ex Karrueche Tran on birthday

Chris Brown didn't ring in his 24th birthday with on-again, off-again girlfriend Rihanna, but he did have another lady close by: ex Karrueche Tran.

Brown celebrated on Friday night at Los Angeles hot spot the Emerson Theatre, partying with a large entourage of pals, a partygoer told us. In addition to friends, our spy said the singer was "surrounded" by beautiful women -- including Tran -- while dancing and drinking at the bash, which was thrown by ZING Vodka and Black Pyramid.

Meanwhile, RiRi, 25, was in NYC over the weekend for her Barclays Center concert, which had to be rescheduled for tomorrow because of the Nets-Bulls playoff game there on Saturday. So, the songstress hit up the game.

Before rekindling their romance this past fall, Brown and Rihanna split up in 2009 after the singer brutally assaulted the Barbados-born beauty. As of late, breakup rumors have plagued the twosome.