The incident took place on Jan. 20 at around 3:55 p.m. near the intersection of Limoges and Guy streets.
Police said the youth was walking home from school when a driver stopped his pick-up truck, got out and watched.
He then got back in his truck and approached the youth near the next intersection, offering a ride. The youth refused and the man drove off in the direction of Claude Street.
A few minutes later, the student saw the same van driving north on De l’Église.
"Even if he didn't commit a crime, the way he act and the fact he asked directly to this young student to climb into his car, we have a lot of worry about that man," said Const.Ghislain Vallières. "What was his intention?"
The man, who police describe as a "person of interest," is Caucasian, about 55 years old, and between five feet seven inches and six feet tall. He was wearing a black tuque, beige pants, work boots and a black coat. He spoke French.
His vehicle was described as gold, two-door pick-up truck that is around 15 years old.
Anyone with information is asked to call Longueuil police.