Thomsen attended Christian Brothers Academy during high school and earned state and regional honors as a member of the soccer team. In 2010, Thomsen joined the New York Red Bulls academy, where he played primarily as a midfielder, and scored 27 goals during his five-year career.[1]
After high school, Thomsen attended the University of Virginia and played 66 games throughout his four-year career, totaling 3 goals and 18 assists. As a freshman, he led the team in minutes with 1,991 as well as assists with eight. In 2014, he played in all 23 matches as a junior and played a crucial role in the Cavilers winning their seventh NCAA College Cup.[2] During his senior year, Thomsen was limited to only eight games due to a sports hernia injury and was sidelined for the remainder of the season.[3]
New York Red Bulls
On December 23, 2015, Thomsen signed a Homegrown Contract with the New York Red Bulls.[4] After only two and a half months with the club, Thomsen was waived before the season on March 7.[5]