He played for German side SpVgg Greuther Fürth between 2005 and 2007. Before playing abroad in Fürth, he broke through in Danish football, playing for Esbjerg fB. He was one of the players who established Esbjerg in the Danish Superliga, in the first five years of the new millennium. After his transfer to Germany, he was a regular in the starting lineup.
In the summer of 2007, he returned to Denmark to play for OB.
Andreasen has played 11 matches, in which he scored two goals, for the Danish national youth teams. He made his debut for the Danish national team on 17 November 2010, in the friendly match against Czech Republic.