Jindo, South Korea (CNN) -- South Korean authorities searched the offices of the company that owns the sunken ferry Sewol on Wednesday, prosecutors confirmed to CNN, broadening a criminal investigation that has already ensnared 11 members of the ill-fated ship's crew.
Investigators also searched the offices of 20 organizations affiliated with Cheonghaejin Marine Co. as well as the home of Yoo Byung-eun, a billionaire whose family appears to control the company, according to the semiofficial Yonhap News Agency.
Yoo is known in South Korea as the "millionaire with no face" because he rarely appears in public. According to major South Korean newspapers, he also has an artistic alter ego -- Ahae -- as a photographer who has won international acclaim.
His website appears to show Yoo taking pictures, but his face is not visible.
Through an investment vehicle and subsidiary, Yoo and his two sons control the shipping company that operated the ferry. Korean tax authorities say that under the family's ownership, the ferry company has been struggling and reported a loss last year.
Days after the ferry sank, the company sent out its president to apologize, but not Yoo -- who's had a brush with bad publicity before.
In 1987, more than 30 people from a religious group were found dead, bound and gagged in a factory outside of Seoul. Officials investigated the incident as a mass murder-suicide, and also investigated whether Yoo had any connection to the event, but determined he wasn't involved.
Prosecutors in the South Korean city of Busan are also investigating the private organization responsible for inspecting and certifying ships for the South Korean government, Yonhap reported.
Investigators are looking for any evidence of possible wrongdoing in relation to the Korean Register of Shipping's safety inspection of the Sewol, the news agency reported, citing an unnamed prosecutor.
The Sewol sank April 16 during a routine trip from Incheon to the resort island of Jeju. Among its 476 passengers and crew were more than 300 high school students on a field trip.
Authorities said Thursday the death toll had climbed to 169, leaving 133 people still missing.
Eleven members of the Sewol's crew, including its captain, have been arrested in connection with the disaster.
Capt. Lee Joon-seok and some other crew members have been criticized for failing to evacuate the sinking ship quickly and for giving orders for passengers to remain where they were. Lee has said he was worried about the cold water, strong currents and lack of rescue vessels.
Lee and others have also drawn public anger for leaving the ship while many passengers remained on board.
Authorities still do not know precisely what caused the incident. It did not appear that the ship was overloaded, according to figures provided by the company and the South Korean coast guard. But coast guard officials said investigators won't know for sure how much cargo the ship was carrying until it is salvaged.
South Korean officials continue to call their operation a search-and-rescue mission, but hopes are fading that survivors may yet be found.
Some 700 divers are participating in the search, according to Ko Myung-suk, a spokesman for the joint task force coordinating the effort. He said 36 fishing boats were positioned around the area to prevent bodies being carried away by currents.
Rescue officials said Wednesday that divers have yet to find an air pocket on the third or fourth decks, where most of the passenger bedrooms and the ship's cafeteria are located.
Rescuers haven't found a single survivor since 174 people were rescued the day the ship sank one week ago.
Many of the bodies pulled from the ferry have come from bedrooms on the capsized ship's fourth deck, said Ko.
Divers had expected to find passengers inside the third-floor cafeteria but failed to find any, the South Korean coast guard said.
While divers still have many rooms to search, no air pockets have been found on either deck, authorities said.
Grief over the sinking has spread across the Korean Peninsula. Even South Korea's nemesis, North Korea, sent condolences Wednesday.
More than two-thirds of those on board the ferry were students from Danwon High School in Ansan, an hour's drive south of Seoul.
On Wednesday, some of their faces stared out from photos amid a huge bank of white flowers at a basketball area in Ansan that has been converted into a temporary memorial.
A permanent memorial is being planned for a park in Ansan.
Hundreds of people filed through the memorial Wednesday, passing about 50 large wreaths on their way to the wall of flowers and pictures.
Somber music played as visitors, including friends and relatives, passed quietly among the tributes. Some wept.
One man, from Seoul, has no ties to the school but came to grieve for the young lives lost.
"I have a daughter," the man told CNN's Nic Robertson. "I think of her alone in black waters. It's just so terrible. I'm angry that I couldn't do anything. So helpless."
The disaster has taken a devastating toll on the high school, where classes are due to resume Thursday.
The school is missing most of its sophomores and a vice principal who was rescued from the ferry but found dead two days after the sinking. He'd apparently hanged himself from a tree.
Lee Seung-min, 17, said one of her closest girlfriends is among the missing. She said she still holds out hope that her friend will return despite the increasingly slim chances of finding survivors.
Before the field trip, the two girls had talked about what universities they might attend, she said.
CNN's Michael Pearson reported and wrote from Atlanta. CNN's Steven Jiang reported from Jindo, and Andrew Stevens reported from Ansan. CNN's Jethro Mullen, K.J. Kwon, Kyung Lah, Tim Schwarz, Larry Register and Judy Kwon also contributed to this report.