Search and rescue teams continued to search overnight for Toronto filmmaker Rob Stewart, who went missing off the Florida Keys earlier this week during a scuba diving expedition.

The award-winning documentarian and conservation activist was diving several kilometres off the coast of Islamorada, Fla., when he disappeared after surfacing Tuesday around 5:15 p.m.

The U.S. Coast Guard, along with several other organizations and volunteers, launched an extensive search effort Tuesday night that has included aircraft, boats and divers, in an effort to find Stewart.

Stewart, who is extremely active in underwater filmmaking, is best-known for his 2006 documentary “Sharkwater,” which examines global shark-hunting and its impact on the ocean ecosystem. The documentary has won more than 40 awards at film festivals around the world.

As the search effort continues Thursday, Stewart’s close friend Dustin Titus said on CTV’s Your Morning that friends and family spent the night organizing volunteers. “We’re in need of more tech divers to get out into the water to try and find Rob,” Titus said.

Another close friend of Stewart’s, Daily Planet host Ziya Tong, said Stewart’s latest dive was part of his work for an upcoming sequel to “Sharkwater” called “Sharkwater: Extinction.”

“Sharkwater: Extinction” is a “huge passion project for him,” Tong said. “I actually heard from him just a couple of days ago, he said he was so happy with the filming.”

Tong said Stewart has “a lot of work to do, and we’re very excited to bring him home and get him back.”

'Deep dive'

On Thursday, Stewart’s sister Alexandra told CTV News Channel that Stewart had been on his third dive of the day when he disappeared, and that it was a “very difficult and technical dive.”

During the dive, her brother and the diver he was with were able to surface, Alexandra said. However, the other diver collapsed unconscious and was pulled onto the boat to receive oxygen. In the ensuing commotion the boat “lost sight” of Stewart.

Stewart’s friend Paul Watson, who is president of the U.S.-based Sea Shepherd Conservation Society, told CTV News Channel Thursday that Stewart and the other diver he was with were using rebreathers, “which can be dangerous.”

Rebreather diving equipment essentially recycles carbon dioxide from exhaled breath, by cleaning it so that the person can breathe the same air again, Watson explained. The equipment is typically used in deep dives.

But the problem with them is that they (can) malfunction,” Watson said. “The damage happens before you even realize it happens.”

Watson said once the boat lost sight of Stewart, “he either drifted away or he sank, we don’t know.”

The search for Stewart is “extensive.” Due to the current, Watson said, Stewart could be “up to 150 miles from where he was last seen.”

Watson said everyone is holding out “hope and doing “everything they can.

“Hopefully we’ll find something.”

'Real inspiration'

Titus said Stewart’s parents are now in Florida and his sister Alexandra, who issued an urgent plea over Facebook for help locating her brother, is organizing search efforts in Toronto. “Everyone is staying strong, staying positive, really hoping for a great outcome on this,” Titus said.

Tong called Stewart a “spectacular human being” and a “real inspiration.”

“There are very few people in the world who have single-handedly become world-changers,” she said. “And that’s what I would say he is.”

Watson said through his filmmaking and activism, Stewart “convinced hundreds of millions of people to look at sharks with a new perception, that they’re not the dangerous monsters. That everybody thinks they’re a part of the ecosystem, we need them.”

He is also known for his documentary “Revolution” and his memoir “Save the Humans.”