Jadianto Nainggolan has barely touched food or got a decent night's sleep since he got word that the ferry was carrying 12 relatives -- including a nephew who was just three years old -- headed home after a party on Monday.
"As soon as I heard I was in shock -- I couldn't eat, I couldn't sleep," he told AFP.
The overloaded boat capsized on Sumatra's Lake Toba in what could be one of the country's deadliest maritime disasters.
Days later, Nainggolan, a power plant worker, cannot believe that four of his siblings and their children could be at the bottom of one of the world's deepest lakes.
The 40-year-old Nainggolan made an arduous 24-hour journey from his home in Jambi province to the picturesque tourist destination after he got a panicked call from his sister.
Now, he is one of hundreds of heartbroken relatives who turn out at search posts or on the lakeshore every morning, praying for news about missing loved ones.
"As soon as we wake up we are thinking about our family," he said.
Just three passengers have been confirmed dead, but official estimates listed 193 others -- including children -- as missing.
The vessel is believed to have been operating illegally with no manifest or passenger tickets and authorities have struggled to pinpoint the exact number onboard when it went down in bad weather.
Many bodies could be trapped inside the sunken ferry, with officials saying that the traditional wooden vessel may have been carrying five times the number of passengers it was built to hold, along with dozens of motorcycles.
Despite a massive search operation involving some 400 personnel, the vessel has still not been located. Toba is some 500 metres (1,600 feet) deep in parts, hampering search efforts. Anxiety -- and anger -- is growing among those desperate for news.
Marasi Gultom said 13 of her family members, including seven brothers, were on the ferry. "It's not normal that there could have 200 people on board and the motorcycles are not allowed," she said.
"That's the fault of the officers -- it was a fatal mistake. Why did they let them board?"
On Friday, authorities turned to sonar technology in a bid to pinpoint the boat's location. Survivor Juwita Sumbayak, who was on the ferry when it went down, said he was reeling from the accident. "My two children are still missing," he told AFP at an area hospital.
Another survivor, Hernando Lingga, 24, recalled the terrifying final moments before the boat disappeared. "Suddenly, water started rushing into the boat," he said.
"Passengers began to panic (and) some screamed hysterically, then the ship began to shake and sunk."