Five aircraft, two from the Malaysian Maritime Enforcement Agency (MMEA), two from the Royal Malaysian Air Force and one from the Royal Malaysian Navy, have joined the effort.
The MMEA said that it had also widening the search area to include the Malacca Strait as well as Sabah and Sarawak waters.
The 7,301-dwt Orkim Harmony (built 2009) lost communication with its owners last week and is believed to have been hijacked.
The tanker left Malacca last Wednesday and was due to arrive at Kuantan port early the next day, but communication was lost just before 9pm local time.
However, Malaysian authorities were not notified about its disappearance until first thing Saturday morning.
The ship was reportedly carrying 5,879t of RON95 fuel worth MYR 21m ($5.5m) which belongs to state-owned oil company Petronas.
The ship also had a crew of 22 people made up of Indonesians, Malaysians and Myanmar nationals.
It was the second Orkim Ship Management-controlled vessel to have been attacked by pirates in the space of eight days.
The 7,119-dwt Orkim Victory (built 2009) was hijacked and had its cargo of fuel siphoned off and stolen in the early hours of 4 June 2015.
