The cotton-top Tamarin monkeys - Rio, Rhia and Pinky - were taken from an enclosure at Drayton Manor Park near Tamworth on Monday night.
It is believed the thieves climbed a perimeter fence and smashed their way into the monkey house.
Trevor Steventon from Staffordshire Police said: "It is not clear why these have been stolen but it was a determined theft."
Rio and Rhia, a breeding pair, have been at the zoo for about 15 years while baby Terry was born in captivity about six years ago.
Their keeper is said to be "very concerned" about their welfare because they need to be kept in conditions above room temperature.
But the animals, native to the Colombian rainforests, are micro-chipped and can be identified if the thieves attempt to sell them on.
The park's managing director Colin Bryan said: "We pride ourselves on our conservation and breeding programme of cotton-top Tamarin monkeys.
"We are extremely concerned and distressed at the theft. The monkeys have a careful daily routine and we employ experts who look after them.
"We need the public's help and information to get them back safely."