Shares in Malaysia Airlines fell 18% to a record low as the search for a missing jet continued for a third day.
A multinational team has been looking for Flight 370 since Saturday after it disappeared en route from Kuala Lumpur to Beijing.
Shares in the firm recovered some of the early fall, but are already down more than 30% for the year.
China Southern, which operated Flight 370 as a code share, also saw its shares fall by more than 3%.
Malaysia Airlines has been struggling as low cost carriers have increased competition in the region.
A planned share swap with budget airline Air Asia was called off in 2012, after pressure from Malaysia Airline’s unions forced the firm to scrap the proposal.
In 2013, Malaysian Airline System, the firm that operates Malaysia Airlines, reported a loss of 1.17bn ringgit ($360m) compared with a 432m ringgit loss in 2012.