11:50 AM PT -- Tamera just revealed her niece Alaina was one of the victims in the attack ... saying, "Our hearts are broken. We just learned that our Alaina was one of the victims of last night's shooting at Borderline Bar in Thousand Oaks."

She continues, "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."

Tamera Mowry is desperately searching for her niece who was at the college bar where a gunman opened fire and brutally killed 12 people.

Tamera's niece, Alaina Housley, was one of just a handful of girls who went line dancing Wednesday night at Borderline Bar & Grill in Thousand Oaks ... this according to a tweet sent by Alaina's friend who added Alaina was the only girl unaccounted for among her friends.

Tamera responded to the tweet saying, "Ashley this is her aunt Tamera Mowry Housley. Can you please DM me your information?" The exchange is pretty heartbreaking ... Ashley replied saying she's been in contact with Alaina's uncle and so far there's nothing new to report.

Tamera's husband, Adam, went looking for Alaina at a local hospital but a reporter tweeted guards wouldn't let him in because the hospital was on lockdown. Making matters worse ... Alaina's Apple Watch and iPhone still showed her location at the bar, this according to the L.A. Times.

Adam told the newspaper, "My gut is saying she's inside the bar, dead. I'm hoping I'm wrong."