Twentieth Century Fox Executive Gavin Smith has been missing for more than a week now, and his family is beginning to open up about the stress of the search.

Smith's three sons spoke with Inside Edition about the investigation, vowing to keep looking until they found him. Because they're worried he may have accidentally driven off a steep cliff on the canyon roads, all three of them have been skipping school to take part in the search, doing their part to cover the city with posters about their father.

CLICK HERE OR SCROLL DOWN FOR UPDATES.

"The problem here is that time is of the essence in these things," said Evan Smith, a sophomore at USC. "My gut feeling is that he is out there and we just have to go find him."

Evan has also been tweeting about the case continuously since his father's disappearance. He shared that the authorities have "combed the canyons" looking for Gavin, and that police have received a lot of tips. Evan is also being honest about the toll the investigation has had on his family's wellbeing.

On Wednesday, he tweeted, "My family and I are not available for interviews. We are drained. Thank you so much for ur help WERE STILL LOOKING!!!" The day before that, he tweeted:

Smith's family launched the website Find Gavin Smith Monday to aid in the investigation. The site has a physical description of Smith, contact information in case he's spotted and a blog that posts updates about the search. It also includes a forum for volunteers who want to pass out posters and join search parties.

Steve Whitmore, spokesperson for the Los Angeles Sheriff's Department, told The Huffington Post Thursday that the department has not encountered any evidence of foul play thus far. The only change to the investigation came Monday, when more resources (like detectives) were added to the case.

"We're doing everything in our power to try to locate this individual," continued Whitmore. "I can't get into specifics, but we're utilizing every resource available and following every lead."

Still, he conceded, just because the LASD hasn't found any evidence of foul play, the possibility "obviously" can't be ruled out.

Deadline and other outlets reported earlier in the week that the case had been elevated from a "missing person's probe" to a criminal homicide investigation, but Whitmore explained to HuffPost there was no departmental distinction between the two.

"It's still a missing persons case," he said. But since "missing persons" is part of the homicide bureau, homicide detectives have been involved from the start.

Smith is a distribution executive for 20th Century Fox who has worked on films like "Avatar" and "Star Wars." In 1975, he played on UCLA's championship basketball team under legendary Coach John Wooden.

The LASD released a description of him as 6-foot-6, 210 lb. man with green eyes, gray hair with blond streaks and a goatee. Other physical markers include a 5-inch scar on his calf and a 4-inch scar on his wrist.

Smith was last seen May 1 at the home of a family friend in Oak Park, Calif. He was wearing purple workout pants and black and gray shoes, and he drove off in his black Mercedes at around 10 p.m. that night. His car is a black 2000 Mercedes 420E with padded storage racks on the roof and tinted windows.

UPDATE: Gavin Smith has walked out on his family at least once before, reports E! Online.

"Thoughts and prayers out to my amazing Mom and my bros plz," Evan tweeted in April. "My Dad decided to leave the family last night. Real Family sticks together."

Evan later deleted the message (see a screenshot) and told E! Online that his parents have never separated.

"They were just going through normal stuff couples go through," said Evan.

Earlier on HuffPost:

Loading Slideshow...
  • May 1, 201: Gavin Smith Last Seen

    Gavin Smith was last seen at his home on the 500 block of Callwood Court in Oak Park, Calif. He left in his 2000 black Mercedes Benz wearing purple pant and black and grey shoes.

  • May 4, 2012: LASD Releases Missing Person Bulletin

    Four days after he was last seen, the Los Angeles Sheriff's Department released a missing person bulletin about Gavin Smith.

  • May 7, 2012: Smith's Family Launches Website

    <a href="http://www.huffingtonpost.com/2012/05/08/gavin-smith-missing-find-gavin-smith-site_n_1501195.html" target="_blank">Smith's family launched</a> the "<a href="http://findgavinsmith.com" target="_blank">Find Gavin Smith</a>" site to get the word out about his physical description, contact information and details about canvassing and search parties. It was last updated May 17, 2012.

  • May 9, 2012: Smith Sons Go Public

    Smith's three sons went to <a href="http://www.insideedition.com/headlines/4329-family-of-missing-hollywood-studio-exec-continues-search" target="_blank">Inside Edition</a> to urge Americans to help find their father. They also spoke about how they were skipping school to help with the search. Check out <a href="http://www.insideedition.com/headlines/4329-family-of-missing-hollywood-studio-exec-continues-search" target="_blank">Inside Edition</a> to learn more about the toll the search was taking on the family.

  • May 24, 2012: Unconfirmed Reports Of A Sighting

    NBC LA reported that locals at tourist destination Morro Bay spotted someone who looked like Gavin Smith at a restaurant. They also claimed he was with a tall female companion. Morro Bay is located on the central coast of California. To see video of interview with Morro Bay residents, <a href="http://www.nbclosangeles.com/news/local/Missing-Fox-Executive-Gavin-Smith-Morro-Bay-Taco-Temple-Sighting-LA-County-Sheriffs-153446535.html" target="_blank">check out NBC LA</a>.

  • June 5, 2012: $20,000 Reward Announced

    Gavin Smith's family offers a $20,000 reward for information that could help bring the missing husband and father home. Check out <a href="http://losangeles.cbslocal.com/2012/06/04/family-to-offer-20k-reward-for-information-leading-to-fox-executives-return/" target="_blank">CBS2/KCAL9 for video</a> of the story.

  • June 9, 2012: Detectives Search Creech Home

    Los Angeles sheriff's investigators search the home of convicted drug dealer John Creech. <a href="http://articles.latimes.com/2012/jun/10/local/la-me-0609-fox-executive-20120610" target="_blank">Cops left with a computer</a>, boxes and a black SUV, reports the Los Angeles Times. Creech lived in the home with with Chandrika Creech, and a lawyer confirmed to the Times that it was in fact the second time police had search the property. Check out <a href="http://losangeles.cbslocal.com/2012/06/21/e-missing-fox-executive-is-romantically-tied-to-married-woman-whose-house-was-searched/" target="_blank">CBS2/KCAL9</a> for footage of the search and comment from Smith's sister.

  • June 10, 2012: Smith Family Continues To Search

    Friends and family continued to search for Gavin Smith in Sylmar, Calif. Sunday because a tower in the area had received the last ping from his cellphone before he disappeared.

  • June 21, 2012: E! News Reports On Romantic Link

    <a href="http://www.eonline.com/news/325213/sources-missing-fox-exec-gavin-smith-had-affair-with-woman-whose-house-was-searched-by-police" target="_blank">E! News reports</a> that Gavin Smith was romantically linked with Chandrika Creech. The pair met in therapy in 2008 and started to have an affair, according to an anonymous source. John Creech reportedly learned of the affair and asked his wife to end it.

  • March 14, 2013: Missing Persons Case Becomes Homicide Investigation

    Police are calling Smith's case a homicide investigation after the discovery of his <a href="http://latimesblogs.latimes.com/lanow/2013/03/gavin-smith-car-found-homicide-case.html" target="_blank">Mercedes Benz in a storage facility</a> linked to John Creech, reports the Los Angeles Times. No body has been recovered.