The 30ft-long blue train, which has two carriages and an orange canopy, was taken after the container was broken into at the Lowestoft seafront in Suffolk.
Police believe a lorry may have been used to remove the train, which disappeared between 4:30pm on 17 July and 10:45am on 18 July.
One Twitter user wrote: “What will the thieves do with it? Repaint it and try their luck in Clacton?”.
Other Twitter users reacted with surprise.
The train runs along the South Beach promenade and is said to be popular with children and families.
Any witnesses or anyone who has information about the train’s disappearance are asked to call Lowestoft police on 101 quoting reference 40241/18.