Investigators are converging on Suncheon, South Jeolla Province in an attempt to smoke out Yoo Byung-eon, the de facto owner of ferry operator Chonghaejin Marine.
After arresting six members of a cult Yoo leads on suspicion of aiding his flight, investigators believe he is still in the area.
Prosecutors are under pressure to find Yoo fast, not only from the public but from President Park Geun-hye, who on Tuesday described the Yoo family's flight from justice "a challenge to our society and a crime."
Park told the Cabinet, "I want law enforcement authorities to quickly round them up, reveal the truth, clarify any suspicions and bring them to justice."
Prosecutors have been grilling the arrested cult members but apparently made scant progress. They searched the house and surrounding area in Suncheon where Yoo had sought refuge and obtained fingerprints of Yoo and cult members who helped him.
On Tuesday, they widened their search, setting up 15 checkpoints and mobilizing around 800 police officers. There are rumors that Yoo is armed.
Major ports are being watched closely to prevent Yoo from escaping by sea. A Justice Ministry official said, "The most common escape route is by ship from Yeosu or Suncheon [in South Jeolla Province] to Dalian and Tianjin in China."