A missing California mother was found dead near the US-Mexico border. Authorities are searching for her estranged boyfriend

Brittney Steenbergen was reported missing by one of her children on Tuesday.

(CNN)A manhunt is underway after a Southern California mother who had been missing for days was found dead near the US-Mexico border.

Authorities are searching for Adel Hussein in the death of Brittney Steenbergen, the Tulare County sheriff's office said Friday.
Hussein is Steenbergen's estranged live-in boyfriend and the father of her children.
      Adel Hussein
      The mother of four and Hussein were reported missing in Plainview, California, on New Year's Eve. One of their children called 911 from their home saying both Steenbergen and Hussein appeared to be missing, the sheriff's office said.
        When detectives arrived to the home, they learned that "a possible domestic violence incident" had occurred, the agency said on Thursday.
          Steenbergen's body was found Wednesday over 300 miles south of Plainview in a rural area of Imperial County, which is along border with Mexico.
          The sheriff's office did not provide details about the condition of Steenbergen's body or how it was found.
          Steenbergen was last seen on December 28 in her Plainview home. Hussein was last seen near Plainview in the town of Tipton on December 31, authorities said.
          On Friday, the sheriff's office said the family's dark blue Toyota RAV4 that was missing from the home was found abandoned in El Centro, California.
            Several law enforcement agencies including the Tulare County and Imperial County sheriff's offices and local, state and federal agencies are working together to arrest Hussein.
            Authorities are asking anyone with information regarding Hussein's whereabouts to call the Tulare County Sheriff's Office at 559-733-6218 or anonymously at tcso@tipnow.com or by text or voicemail at 559-725-4194.