It was the second such attack this week.
About 60 policemen were on duty at the post in Pashupatinagar in Ilam district when hundreds of rebels stormed it around 10.45 pm (1700 GMT) on Wednesday, a police spokesman said.
"About a dozen policemen are safe while the rest are still missing," he said. "We have sent reinforcements and a search is underway."
Authorities say the rebels, who are fighting to topple Nepal's constitutional monarchy and establish communist rule, usually ask policemen who surrender after attacks to carry loads for them as they return to their bases.
"They (rebels) also attacked a state bank, a government office and ransacked several shops and fled," Binita Chhetri, a Pashupatinagar resident, said by phone.
Ilam, a tea-growing region, is about 600 km east of Kathmandu and borders Darjeeling in eastern India.
The Wednesday night raid came as life across Nepal was crippled for a third day due to a general strike called by the guerrillas.
The rebels also set off two bombs in Kathmandu late on Wednesday, wounding four people.
Earlier this week, they raided a police post in Yadukuwa, also in east Nepal, killing nine policemen. The revolt has cost more than 9,300 lives since it began in 1996.