Police in Utah have launched a search for Michael Cavallari after his 2014 Honda Civic was found abandoned by the side of the Interstate 70 in Grand County on 27 November (15), the day after America's Thanksgiving holiday.

The 30 year old has not been seen since, and authorities have appealed to the public for any information as to his whereabouts.

Kristin, who welcomed her third child with her husband, American football star Jay Cutler, just four days before Michael went missing, made no mention of the family drama on her social networking pages before the news hit headlines on Sunday (06Dec15), and now she has reached out to followers to express her thanks for their kind words.

"I appreciate the thoughts & prayers that have been extended to me & my family," the former The Hills star writes on Monday (07Dec15), beside a photo of the siblings on a beach during their youth. "We remain hopeful and I will share any news that we receive. I have such gratitude for those that have shared their support."

Grand County Sheriff Steven White revealed over the weekend that Michael's laptop and cell phone had been found in the abandoned car, which appeared to have hit a large rock on the roadside, but the reason for his disappearance remains unclear.

"We're combing the area for anything we can find," White told deseretnews.com. "We're deeming it suspicious, but there's nothing to indicate anything one way or another. The vehicle was just abandoned."