Officials said the Karachi-bound aircraft, operated by the private carrier K2 Airways, reported a navigational system issue while flying from Sharjah in the United Arab Emirates with five people on board.
The search is ongoing, according to three officials familiar with the rescue operation.
They said the vast search area in the Arabian Sea and rough monsoon seas posed significant challenges to the search-and-rescue operation.
There has been no official confirmation of the aircraft's fate.
In a statement, K2 Airways said search and rescue operations were still being conducted by Pakistani authorities and the company was co-operating fully with aviation authorities.
"We continue to pray earnestly for the safety of our colleagues," it said.
Earlier, Pakistan's Airports Authority said on X that radar data showed the aircraft making a sharp change in heading and rapidly descending before radar and radio contact were lost about 9.21pm on Tuesday, about 287km west of Karachi.
According to the authority, Pakistan's military and civilian agencies activated the Rescue Co-ordination Centre and launched search-and-rescue operations at sea shortly after the aircraft went missing.
According to the officials, Pakistan naval frigate PNS Zulfiqar was dispatched to the area where contact with the aircraft was lost.
The Pakistan Air Force also deployed aircraft to assist in the search, while a Pakistan Navy ATR aircraft took off from the southwestern city of Turbat.
A merchant vessel operated by the Pakistan National Shipping Corp also joined the operation, officials said.
Aviation expert Imran Aslam told local broadcaster ARY News late on Tuesday that it remained unclear what caused the aircraft to disappear from radar.
He said that even if an aircraft suffered an engine failure, it would usually continue gliding rather than plunge suddenly.
He said the exact cause would become clear only after investigators gathered more evidence.
In May 2020, a Pakistan International Airlines flight carrying 98 people crashed into a densely populated neighbourhood near Karachi airport while attempting to land.
All but one of the 99 people on board were killed.
A government investigation later concluded that human error by the pilots and air traffic controllers caused the crash.
