Police are investigating the disappearance of four family members who have lost contact with relatives since April 10 during a Songkran trip.

Nirut, 41, and his wife, Narumon, 41, left their home with two children, 12 and 7, in a grey pickup truck on April 6 for the holiday. The couple's eldest daughter, 19, who studies in Chiang Mai, did not travel with them.

She and relatives were unable to reach any of the four after April 10, prompting them to file a report with police.

The family's disappearance has drawn public interest after their pickup truck turned up at a used car dealership in Udon Thani and their phone numbers were cancelled in Bangkok's Lat Krabang district. The fate of the four is still unknown.

When the pickup truck turned up at the dealership, officers found the vehicle had been sold four times before ending up at the location. The car was registered in Ms Narumon's name, who apparently sold it on April 7 before it was handed over to a buyer at a gas station in Phitsanulok.

Before the disappearance, the couple raised a huge amount of funds from villagers, saying the money was for a business investment which they did not disclose.

The used car dealer purchased the car from a 33-year-old man for 422,000 baht on April 9.

The person who bought the truck from Ms Narumon reportedly transferred 385,000 baht to her account at 3.40pm on April 7. She told the buyer she wanted to sell the car due to loss of income after the Covid-19 pandemic.