A 28-year-old California woman who has been missing for more than a week allegedly told her stepdad she was headed to the gym – and hasn't been seen since, according to family members, who are pleading for the public's help finding her as some fear she may have harmed herself.

Sara Celeste Otero was last seen on Jan. 28 at around 8:40 a.m. at the 1200 block of Aldernay Court, in Oceanside, about 40 miles north of San Diego, according to local police.

Her phone has been off since 10 a.m. that morning, relatives told Fox News Digital.

"We've got very little details," Otero’s step-brother, Ryan Bear, said Monday. "And that's the entire reason that we're trying to ask the public for any and all information at this point, because we don't know anything."

(Courtesy: Ryan Bear)

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She left her mother’s house late last month after telling her stepfather she was headed to the gym, her stepsister, who uses only her first name Chelsea, said Monday. But she never arrived at the gym -- and the friend she said she was meeting told the family she had no idea about a plan to meet that day for a workout.

Bear said he believed Otero planned to take some alone time at a local beach. But she failed to show up for her work shift that evening – something completely out of character, he said.

"She had never missed a day of work," he said.

Otero’s boyfriend was at work at his own job the morning she went missing, according to Bear, and is just as broken up as the rest of the family.

"He’s in just as much shock as we all are," he said. 

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Chelsea said she’s only met the boyfriend over Zoom because of the coronavirus pandemic. The two had only been dating for a short time and had "been going through some stuff," she said, but she did not suspect foul play.

"He’s pretty devastated," she said. Of Otero, Chelsea said, "She’s grappling with a lot, she shared that she was feeling depressed…it’s affected their relationship."

She said she was worried her stepsister may have harmed herself.

In addition to grappling with depression, Otero had struggled with substance abuse in the past but has been clean for two years, according to her siblings.

Bear said his whole family grew up "very outdoorsy" and that his step-sister often spent time in nature.

She had sometimes been reclusive, but cutting off communication with her family for any length of time is not normal, Bear said.

"To be missing for a few days and not answering family, that’s just never happened before," he said. "You’re loved. You’re cared for. Your family just wants to know that you’re safe and sound."

Police described Otero as 5 feet, 6 inches tall and weighing 130 pounds. She has blue eyes, long brown hair and several tattoos. One shows a flower on her arm, another says "It’s in our nature" on her right bicep and she has "Winnie the Pooh" on her ankle.

She wears glasses and was last seen in a green "military-style" jacket with bronze pants.

Police said she may be traveling in a charcoal gray Subaru Outback with California license plate 7GAB955.

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It’s unclear where she may be headed. She has ties to Boise, Idaho, where she lived until 2019, and she enjoyed spending time at Joshua Tree and in Costa Rica, according to Chelsea.

Bear said the family has no information about anywhere specific to search.

Anyone with information on Otero’s whereabouts is asked to call Oceanside police at (760) 435-4900.

The family is asking for anyone with any information on Otero’s whereabouts, however small, to come forward.

"Please come back and let us know you’re safe," Chelsea said.