In the capital Skopje, thousands of sobbing fans gathered in the main square, lighting candles and leaving flowers, teddy bears and posters of the 26-year-old pop star in makeshift shrines.
The government said the day of Proeski's funeral would be a day of national mourning and awarded him the title "Honorable citizen of Macedonia". It cancelled its sessions for the day, and sent a delegation to Croatia to recover his body.
"We all couldn't help but love Tose Proeski," said Macedonia's President Branko Crvenkovski in a statement expressing his condolences to the singer's family.
Croatian police said Proeski's vehicle hit the back of a truck and crashed into the protective fence on the Zagreb to Belgrade highway near Nova Gradiska, 120 km (70 miles) east of Zagreb. He was asleep in the passenger seat.
Two other people in the car were injured.
Macedonian television stations interrupted their regular programs with news of the accident.Proeski, a classically-trained singer, started his pop career at 15, releasing his debut album at 18
His boyish good looks and passionate delivery made him a regional favorite. He had several number one hits in Macedonia, Serbia, Bosnia and Croatia with songs such as "Cija si" (Whose Are You) and "Ako me poglednes vo oci" (If You Look Me In The Eyes).
He sang in Macedonian and Serbian and represented Macedonia in the Eurovision Song Contest in 2004.
He was also a UNICEF goodwill ambassador and toured the Balkans to promote humanitarian projects.