He started his career with Hannover 96 where he played 79 games before moving to Schalke in 1999. He played over 250 games for the club over 11 years with the team. On 1 June 2010, Asamoah signed a two-year contract with the then Bundesliga-promoted club St. Pauli. In June 2011 he terminated this contract. From 12 July 2011 on, Asamoah was at VfB Hüls, keeping himself fit. After six months without a club, Asamoah signed for SpVgg Greuther Fürth on 10 January 2012. Asamoah won the league title with SpVgg Greuther Fürth and played in the Bundesliga in the 2012–13 season. On 15 July 2013, it was announced that Asamoah will return to Schalke 04 as player for Schalke's second team.
Asamoah is married and has two children, twins Jada and Jaden (born 26 February 2007). He suffers from a heart condition, hypertrophic non-obstructive cardiomyopathy. In his case, the flesh lobe that separates the right and left heart chambers is extremely thick, which can cause an arrhythmic heartbeat. Asamoah's brother Lewis last played for 1. FC Wülfrath and his cousin Emmanuel plays for the U-17 of FC St. Pauli.