A neighbor's surveillance camera captured the last known moments of a Texas teenager who vanished without a trace on Christmas Eve.

Camila Mendoza Olmos, 19, was last seen at 6.58am on Wednesday, after leaving her home in northwest Bexar County, a region on the outskirts of San Antonio that has long been flagged by authorities as a human-trafficking corridor.

Surveillance video obtained by KENS showed an individual believed to be Mendoza Olmos standing near her vehicle with the lights on.

She appeared to search inside the car for an unidentified item, investigators said. Moments later, the footage ends. 

Her car was still parked at the home, leading authorities to believe she left the area on foot. She has not been seen since.

The teen's loved ones confirmed she typically goes for a morning walk, but always takes her phone with her - a routine that made her sudden disappearance all the more alarming.

Authorities say the only items Mendoza Olmos is believed to have had with her were her car keys and possibly her driver's license. Her phone was reportedly turned off and left in her bedroom.

A CLEAR Alert, the statewide system for locating missing and possibly endangered adults, has been issued for the teen as more than 100 people joined the desperate search for her.

Camila Mendoza Olmos is 19 years old and lives in northwest Bexar County, Texas. She was last seen around 7am on Wednesday, Christmas Eve

Footage from a neighbor's surveillance camera showed an individual believed to be Mendoza Olmos standing near her vehicle with the lights on. She appeared to search the inside the car for an unidentified item, investigators said. Moments later, the footage ends

Deputies described Mendoza Olmos as 5ft 4in tall, weighing about 110 pounds. 

She was last seen wearing a baby blue and black hoodie, baby blue pajama bottoms and white shoes. 

Authorities have not shared any evidence of foul play, but the circumstances, including her abandoned phone, her sudden disappearance on foot, and the lack of any confirmed sightings, have fueled growing concern. 

The teenager's best friend, Camilla Estrella, told KSAT how the pair would 'always be on the phone together when she walks'.

Another close friend, Isabela, described Mendoza Olmos's behavior as being 'very out of the norm.'

'It's not like her. She's always been the one to always stalk on us and like, "why aren't you doing this?" [She would] make sure that her phone's always charged,' Isabela added.