Chalfant Valley, California - It has been many years since California teen Karlie Lain Gusé vanished from her home in Chalfant Valley. She is still yet to be found, and few updates are coming our way regarding the potential crime that sits behind this mystery.

Karlie was 16 years old when she moved in with her dad Zachary and her stepmom Melissa in August 2018.

According to Crime Online, she had previously lived with her mother, Lindsay Fairley. However, when Fairley moved, Karlie decided to live with her dad so that she could stay close to her friends.

At first, everything appeared to be going smoothly. She was known as a fun and loving friend, as Kolo 8 reported. Though Karlie could be quiet and introverted, she was popular among her classmates.

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However, around the time of her disappearance, everything started to change.

A friend of Karlie's told Fox News that in the days before her vanishing, she experienced frantic "episodes" during which she would get paranoid about being tracked via her smartphone.

On the evening of October 12, 2018, one day before she disappeared, Karlie asked her stepmom if she could attend a football game at her high school.

However, after Melissa granted her permission, she went to a house party instead.

At around 8 PM, Melissa called and asked Karlie if she needed a ride home from the game, but the teen told her that her boyfriend would be driving.

Shortly after the call, people at the party recalled Karlie suddenly beginning to panic and becoming inconsolable.

Only thirty minutes after talking to Melissa, Karlie picked up her phone once again and dialed her stepmother's number, asking to be picked up as she was "scared".

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Worried sick, Melissa got into her car immediately. However, when she arrived at the party, her stepdaughter was nowhere to be seen. She then started searching the area and quickly noticed a small light – it was Karlie who was running down the street with her phone in her hand.

When she spotted her family's truck, Karlie jumped into it and told her stepmom that she was terrified.

Suspecting that Karlie's condition was an adverse reaction to something she had taken at the party, they decided that she didn't need to go to the hospital.

Instead, Melissa stayed with Karlie in her room until the early hours, painting nails, reading the Bible, and chatting until 3 AM.

Melissa recorded Karlie during these activities and planned to show her the footage the next day.

Melissa initially stated that she'd gone about her usual routine the next morning, after waking up at 5.45 AM and getting the kids ready for school. When she opened Karlie's door, though, she found the bed empty.

In a later interview with Dateline NBC, however, Melissa changed the record on how things happened that morning.

Melissa actually woke up briefly at 5.48 AM and saw Karlie awake next to her before falling back asleep. It was only when she woke up again between 7.15 and 7.30 AM that she noticed her stepdaughter was gone.

Melissa and Zachary then began driving around the neighborhood, looking for her, as they hoped that she had gone for a walk to clear her head.

At around 9.35 AM, they called the police.

When officers arrived at the Gusé's house, they found no indication of forced entry and also noticed that all of Karlie's personal belongings, including her cellphone, glasses, and cash, were left behind.

Three possible sightings were quickly brought to the attention of authorities from neighbors who think they saw Karlie with a piece of paper in her hand.

She was reportedly last seen walking south toward Highway 6.

According to Carson Now, the Sheriff's Office conducted a week-long search that included sniffer dogs, helicopters and ground resources.

However, on October 25, their efforts were officially suspended.

After that, private search parties were held and posters with Karlie's image and description were put up all across eastern California.

A week after she went missing, the Sheriff's Office even set up a checkpoint along Highway 6. Sadly, no one recalled seeing anyone matching her description.

In December 2018, bloody underwear was found during a search of the area, along with some coyote scat nearby. The item was collected for testing, but not sent to the proper forensic facility. Police have since stated that they do not believe the underwear is connected to the case.

Over the last few years, a number of people have reported to have found Karlie Lain Gusé in California and Nevada, but none of them have turned out to actually be her.

To this day, Karlie Lain Gusé's disappearance is being investigated as a missing person's case. Police currently have no theories as to what happened.

Karlie's birth mother Lindsay Fairley fears her daughter may have overdosed on a drug the night before she went missing. In an interview with Dr. Phil, she hinted that Melissa may have awoken to find Karlie dead next to her.

However, Melissa denies this and any involvement in Karlie's vanishing.

At the time of her disappearance, Karlie Lain Gusé stood at 5'7" and weighed 110 pounds. She has brown hair and blue eyes, and her left nostril is pierced. She is believed to have been wearing a white t-shirt, Vans shoes, and either dark gray sweatpants or a pair of skinny jeans.

She would be 19 years old today.