The niece of Sister Sister actress Tamera Mowry-Housley and her husband Adam Housley has been killed in the mass shooting at a Southern California bar.

"Our hearts are broken," the pair said in a joint statement. "We just learned that our niece Alaina was one of the victims of last night's shooting at Borderline bar in Thousand Oaks. Alaina was an incredible young woman with so much life ahead of her and we are devastated that her life was cut short in this manner. We thank everyone for your prayers and ask for privacy at this time."

The couple were searching for their niece, Alaina Housley, earlier after seeing on twitter that she was missing.

They first responded to a tweet from a suitemate of Alaina who said her friend was missing and offered a description of what she was wearing.

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Mowry-Housley responded by identifying herself as Housley's aunt and sought to contact the suitemate directly.

Authorities say a gunman killed 12 people, including a sheriff's sergeant, Wednesday night (local time) at Borderline Bar & Grill in Thousand Oaks.

Housley's suitemate said on Twitter that Housely was among a group of women who went dancing at the bar and has not returned.

Mowry-Housley's husband, former Fox News correspondent Adam Housley, also took to Twitter to ask: "Please pray if you believe....pray."

According to the Los Angeles Times Housley tried to look for his niece at around 3:30 am but was turned away because the hospital was on lockdown.

The gunman, identified as 28-year-old Ian David Long, opened fire during college night at a Thousand Oaks country music bar, killing 12 and sending hundreds fleeing before apparently taking his own life.