Sami Aslam and Farrukh Saleem disappeared on Thursday night after they went to visit a water park in the Gulshan-e-Maymar area on the outskirts of Karachi.
Police official Nawaz Tanoli said there were strong indications that the duo might have been kidnapped.
"Some parts of this area have dacoits in hiding who carry out kidnapping for ransom," he said.
Tanoli said the police were coordinating with the UNICEF (United Nations Children's Fund) office whose spokesperson Vittorio Cammarota today confirmed in a statement that the two local workers of the UN body had gone missing.
More From This Section
The two officials belong to Hyderabad city and were on a visit to the water park.
The disappearance of the two workers was reported by the wife of one of them after she couldn't contact her husband on his cell phone.
In the past also, UN workers have been targeted by militant groups in anti-polio drives on the outskirts of the city which is plagued by ethnic, sectarian and militant violence.