The two men were kidnapped in December by a group in the Niger Delta.
Major Musa Sagir, a spokesman for a joint military force tasked with policing the Niger Delta, said troops had been deployed to hunt for the kidnappers who seized the Dutchman.
The foreign ministry in The Hague confirmed the man abducted in Port Harcourt was Dutch but would not release his name.
A Dutch national was killed in the region just over two months ago when gunmen attacked a boat travelling between Port Harcourt and the oil-and-gas terminal at Bonny.
The most high-profile of the separatist groups operating in the region, the Movement for the Emancipation of the Niger Delta (MEND), has abducted dozens of people in the past but said it was not involved in the latest attacks.
About 60 foreigners, most of them linked to the oil industry, have been kidnapped in Nigeria since the beginning of the year. Most have been released unharmed.
A mixture of criminal gangs trying to raise money through ransom demands and separatist groups seeking greater autonomy for the oil-rich region have carried out previous kidnappings.
Kidnappings and attacks in the region have forced oil companies to reduce Nigerian output by about 20 per cent since February 2006.