From 2005 till 2012 Rieks played at hometown club Esbjerg fB.
NEC
In July 2012 he signed a three-year contract at Dutch side NEC.
IFK Göteborg
On 10 August 2014, Rieks joined Swedish side IFK Göteborg on a three and a half year contract.[1] Having scored 21 goals in 92 appearances, Rieks left the club upon contract expiry at the end of the 2017 season.
Malmö FF
On 12 January 2018, Rieks signed for reigning Swedish champions Malmö FF on a three-year contract.[2] This marked a rare direct move between IFK Göteborg and Malmö FF, the two historically most successful Swedish clubs.
International career
Rieks was called up for the Denmark national team in March 2009 for the two games against Albania and Malta. This was his first call-up.[3] He has been called up afterwards, and he had his international début against South Korea on 14 November 2009, and on 18 November 2009 he had his second international match, where he also scored his first international goal.