Demba-Nyrén arrived in Sweden as a nine-year-old and grew up playing for
Falun-based clubs
Slätta SK and
Falu BS. He ventured into the
Allsvenskan with
BK Häcken in the early 2000s, spending two seasons before turning professional with Greek club
PAS Giannina. His career took a significant turn when his coach moved to
Aris, bringing Demba-Nyrén along, where he impressively scored 12 goals in 22 matches. Subsequent seasons were marred by injuries and a dip in form. After an unsuccessful stint in Bulgaria with
Levski Sofia, he joined Greek powerhouse
Panathinaikos, yet failed to make a significant impact. During his tenure at Panathinaikos, Demba-Nyrén experienced success by clinching the
domestic double with the club. Additionally, he had a four-month loan spell at
Kerkyra. Demba-Nyrén was brought to Denmark by
Esbjerg fB in 2005, quickly establishing himself as a standout player for the team. During his two-and-a-half seasons with Esbjerg, he scored 21 goals in 61 league appearances, earning a reputation as one of the club's finest players in its history. His impressive performance led to a transfer to Norwegian club
Brann in the winter of 2007–08, for a reported fee of around DKK 9 million, with potential additional payments based on performance. He signed a four-year deal. In January 2009, he moved to
OB from Brann as part of an exchange deal, with
David Nielsen moving in the opposite direction. However, by February 2011, Demba-Nyrén was released from his contract with OB. On 4 March 2011, Demba-Nyrén signed for
Notts County on a contract until the end of the season. He scored his first and only goal of the 2010–11 season in a 3–1 defeat against
Dagenham & Redbridge. On 16 May 2011 the club announced Demba-Nyrén would not be having his contract renewed. In August 2013, Njogu made the decision to join
Ettan club
Dalkurd FF following his departure from
Superettan club
IK Brage. During 2014, Njogu played for
Falu FK. On 4 June 2015, he signed a trial contract with
Dalhem IF, a
Division 3 club based in
Gotland. He showcased his talent by scoring five goals for the club in 2015, ==Coaching career==