However, rescue team members who entered the cave found footwear thought to belong to the young footballers of The Ban Phong Pha team, which is known in the area as "Moo Pa" (wild pig).
Rescue teams search the Tham Luang caves for 13 members of an under-16 soccer team, in the northern province of Chiang Rai, Thailand, June 25, 2018.
"They haven't eaten anything since Saturday, so we have brought them food and drink".
The search began around midnight on Saturday after police received a report of a missing child from a mother who said her son had not returned from the soccer practice that evening, ThaiPBS reported.
Investigators believe the team, which has been missing since Saturday, crawled into the Tham Luang Nang Non Cave through a narrow 15-meter long channel.
The group were apparently trapped when a heavy storm flooded a stream at the cave's entrance.
"We think they are in this part of the cave, which continues for another three kilometres", Mr Pasakorn Boonyalug said.
The rising water frustrated efforts by the rescuers, including navy SEALs, to search farther in the cave, which is thought to be about 6-8 kilometers (4-5 miles) long and contain some large chambers.
"The team went down to a depth of 5 metres and found a large chamber. but we've found no trace of the children", the navy unit said on its Facebook page.
"Right now, our family is hoping that the children trapped inside will have formed a group and are safe and waiting for officials to go in and save them in time", he said.
The cave is a tourist attraction but can flood during Thailand's rainy season, which runs from June to October. "That's what I'm hoping", said Noppadol Kantawong, the father of one of the missing boys.
He said footprints and handprints were found inside the cave complex and that officials believe the boys are still alive.
But when searchers got to the entrance, they located only a motorcycle and 11 bicycles, along with backpacks, soccer shoes and other sports equipment.
Local media reported that the team is believed to have entered the cave after a practice session, before a flash flood trapped them in the rock structure as rising waters blocked their exit.