The family of a University of California, Berkeley student, who hasn't been heard from since Thursday's terror attack in Nice, are traveling to France, hoping to find him.

On Saturday, NBC News confirmed that Nicolas Leslie's father, Conrad, left his home in Del Mar and was headed to the airport. He was accompanied by two other people.

An attacker, identified as 31-year-old Mohamed Lahouaiej Bouhlel, a Tunisian citizen living in Nice, is accused of driving a truck through crowds leaving a Bastille Day fireworks celebration, killing 84 people and injuring scores other.

Nicolas Leslie, 20, was among 85 Berkeley students attending a study abroad program nearby, officials said Friday. Three other Berkeley students in the group were injured in the attack, in which a gunman drove a truck through crowds leaving a Bastille Day fireworks celebration in the seaside tourist destination.

According to the San Francisco Chronicle, French officials are refusing to identify people who were injured Thursday and are undergoing treatment at local hospitals.

"We’re trying to get ourselves to France right now," Conrad Leslie, Nick’s father, told the Chronicle. "We’re going crazy."

The Wall Street Journal reported that Leslie's uncle, Fabeo Bottini, has been going from hospital to hospital in Nice trying to get information about his missing nephew.

Friends told NBC Bay Area that Leslie avoided being hit by the truck in Thursday's attack but was separated during the stampede and chaos that followed. They also say he was active on social media after the attack but has been silent since, which they describe as unusual.

Bay Area Mourns Bastille Day Attacks

Leslie is from Del Mar in San Diego's North County and attended Torrey Pines High School, according to his Facebook page.

NBC News spoke with a neighbor Saturday who has lived near the Leslie family for many years in Del Mar.

Geert Schmid-Schoenbein said he was shocked to learn that Leslie is missing after the attack in Nice and can’t wrap his head around the fact that someone he knows was involved in such a horrific event.

"The fact that this kid goes on an education abroad trip to France and goes there to a celebration and is entangled in an event like this – and hopefully survives – is beyond any probabilities that one can ever think of," Schmid-Schoenbein said.

The neighbor said he has nothing but "good memories" about Leslie and his family. Schmid-Schoenbein said he has watched Leslie grow up -- from the day his parents brought him home from the hospital to Leslie getting his driver's license and going off to study at Berkeley.

“It breaks my heart,” he said. “This is just frightening. I’m speechless.”

Schmid-Schoenbein said Leslie is an only child who often returned to Del Mar to visit his family. He remembers Leslie, who many call Nick, as a nice young man who was active in sports and did well academically.

"We never heard any problems about Nick. We saw with great enthusiasm that he was going up to Berkeley," he told NBC News.

Schmid-Schoenbein said Leslie's parents have always been fully devoted to their son and very supportive of him.

"Nothing else but a wonderful family," he added.

Schmid-Schoenbein said Leslie's mother is originally from Italy.

Leslie is currently a junior at UC Berkeley, majoring in the College of Natural Resources.

UC Berkeley spokesperson Robert Sanders said that campus study abroad, risk services office and student affairs staff were working with fellow students in France, the program director on the ground, local officials, U.S. consular officials and Leslie's family to find him.

The Daily Beast reported, however, that a friend of Leslie’s saw the college student running through the streets of Old Nice. But Leslie's aunt, Bottini’s wife, said the student never returned to his student housing Thursday night.

Leslie's friend, Anoop Baliga, has been reaching out to Leslie via social media along with many others hoping to hear from him soon. Baliga says Nick's last Snapchat story post was from a restaurant about 10 minutes away from the attack's location. He says there has been movement on Nick's Facebook page, but he thinks it's because people are using his laptop to try and find him.

Chandrabh Akireddy, who knows Leslie from the Net Impact Berkeley Undergrad program at UC Berkeley, said a couple of his friends who were in the square with Leslie checked in after the attack.

"Some people saw him escape ... One of the students said he ran off with Nick during the attack but they got separated," Akireddy said. "The guess seems to be that he is OK."

Akireddy's friends saw Leslie active on Facebook messenger after the attack. "We're taking that as a good sign and hoping that his phone died or something, and that he's still hiding somewhere," he said. "He's a great guy, we're optimistic."

Akireddy said he met Leslie after joining Net Impact last year.

He said that Leslie spent his childhood between San Diego and Italy.

Mustapha Khokhar, a friend of Leslie’s at UC Berkeley, said he received a Snapchat from Leslie at 1:20 p.m. PT Thursday, but that he hasn’t heard from him since. That radio silence is odd for someone who has been snapchatting — or “streaking,” as its often called — relentlessly over the course of his vacation.

“We had a 20+ day streak going,” Khokar said. “He’s been essentially documenting his whole trip to me over snap. And that streak ended yesterday.”

Khokar said it’s possible but out of character for Leslie to have accidently let his phone die.

“Nick isn’t the type to go AWOL and pass out with his phone dead,” he said. “The dude is attached to his phone…but I would hope that’s what happened.”

Khokar, who has known Leslie for more than two years, described his friend as someone with a “heart of gold.”

“He’s one of the most genuine and sincere people I know,” he said. “If you need help with work he will be there. If you call him at 3 a.m. asking to be picked up ‘cause you’re drunk, he will be there.”

According to Sanders, two of the students — identified as Diane Huang, 20, and Daryus Medora, 21 — suffered broken legs and were receiving treatment at a hospital in Nice.

A third, 23-year-old Vladyslav Kostiuk, suffered a broken foot.

Kostiuk posted a photo of his injury on his Facebook page, with the caption: "I would say only one thing: I was lucky, I'm alive, unlike other people that were walking with me. Just got out from a surgery. Picture: in a casino where I was taken first."

Paige Basconcillo, a Berkeley student from Bakersfield, California, who is also in the Study Abroad group, has been tweeting about Leslie as well, asking people in Côte d'Azur (the French Riviera) to search for him.

All of the students in the study abroad program were attending a 15-day program on Entrepreneurship and Innovation in Europe, part of the international European Innovation Academy, which was suspended to observe the national three days of mourning in France.

The program will go on through its planned end date of July 24, university officials said, but the campus has offered to bring home any students who wish to leave. So far, three students have opted to return home to the U.S.

University Vice Provost Cathy Koshland and Dean of Students Joseph Defraine Greenwell joined the Bay Area community to express sympathy to to all the students, families and the French community who have been affected by this “tragic event” and “senseless violence.”

A message posted by UC Berkeley student Abhinav Kukreja on Facebook talks about Leslie missing since Thursday's attack.

"We know he successfully avoided colliding with the truck, but we lost him during the stampede and chaos that follow. Please share this so Nick an get back to his friends and family," Kukreja wrote.

Recent terrorist attacks have impacted several UC Berkeley students. Berkeley sophomore, Tarishi Jain, was among 20 hostages killed by Islamist militants in Dhaka, Bangladesh on July 1.