 Thoresen started his career with his hometown Storhamar Dragons before he shifted to Canada and played junior hockey for two teams in the QMJHL, the Moncton Wildcats and the Baie-Comeau Drakkar.In the 2002–03 season, while a member of the Drakkar, he had 108 points in 71 games played, good enough for second in team scoring.His 75 assists that season were best in the QMJHL.