The original reward was set to expire Sunday and the renewal extends the offer for at least another 90 days.
David Cheng Wang, 60, and his 57-year-old wife, Marian Mei Chung, were found dead in their home in October.
Police believe they were killed during a robbery.
The city of Diamond Bar is also offering a $10,000 reward.
Anyone with information was asked to call sheriff's homicide Detectives Margarita Barron or Dameron Peyton at (323) 890-5500.