Dante disappeared while walking the dog near his home in Tröingeberg, Falkenberg, at 5pm on Tuesday. The dog was later found.
“The parents don't think the boy knows the way home by himself,” said police spokesperson Peter Adlersson.
The 12-year-old has a history of going missing, but has never been gone this long. By 4pm on Wednesday he had still not been found, despite police, volunteers and the Armed Forces searching for him.
Non-profit organization Missing People told Aftonbladet that around 1,000 people had joined the search.
There were no immediate signs the boy had fallen victim to a crime, but at 3.25pm on Wednesday police said they had launched an investigation into kidnapping. They said the reason was that they did not know where he was or how he had gone missing and a formal probe makes it easier for police to investigate the matter.
He was dressed in a blue coat with a hood and black shoes at the time of his disappearance. He is around 140 centimetres tall, slim and with blond hair to his ears.