Kristin Cavallari's Brother Reported Missing After Suspicious Car Crash & Arrest With Gun

Investigators are working together to solve the mystery of Kristin Cavallari's missing older brother, Michael. No one has reportedly heard from the former MTV reality star's brother since his car was found abandoned on a suspicious dirt road in Grand County, Utah on Friday (Nov. 27), according to Page Six. The incident took place just days after he was arrested while possessing a gun.

A rancher found Michael's car with the engine running and the air bag deployed in Utah, Grand County Sheriff Steven White told Page Six. It was located in a part of the state known for its national parks, just 200 miles south of Salt Lake City and five miles south of Interstate 70.

Police were able to trace the car back to him based on store receipts found in the car. A few hours before his abandoned car was discovered, surveillance cameras place his car at a convenience store in Monticello around 3:30 a.m. that Friday.

 I appreciate all the concern, thoughts, and prayers that have been extended to me and my family. We remain hopeful and I will share any news that we receive. I have such gratitude for all those that have shared their support.

A photo posted by Kristin Cavallari (@kristincavallari) on Dec 7, 2015 at 7:33am PST

Authorities believe he was driving alone and unexpected hits to large rocks and washes caused his 2014 Honda Civic's air bag to deploy. White revealed search crews have been relentlessly looking in the area by foot and helicopter, but so far have no trace of Michael. Foul play has been ruled out.

Four days prior (Nov. 23), the 30-year-old Southern California resident was arrested by Orange County law enforcement on suspicions of making criminal threats with a shotgun to an unnamed woman. The woman reportedly told police they had an argument days before his arrest. She claims he later returned to her apartment with a loaded gun.

Police said Michael's breath smelled of alcohol when they arrived on the scene and he admitted to having a loaded shotgun in the trunk of his car. He denied the woman's allegations, posting bail on Nov. 25.

Kristin, who rose to fame after starring on teen series like Laguna Beach and The Hills, posted a sincere photo to Instagram on Monday (Dec. 7), thanking everyone for their concern and support.

Michael Cavallari's father and stepfather are both in Utah helping authorities with the search, according to White.