West Yorkshire Police has been looking for the weapon since February, when it was shown to be missing during an audit of the force’s training equipment.
The force said an “extensive search” was being carried out to recover and account for the Taser, which would normally be stored at its training ground in Leeds.
A spokesman said: “While the likelihood is that the Taser is on police premises, the force is taking the step of making the public aware on the off-chance that they have any information about its whereabouts.
“Training Tasers use batteries that have already been depleted by use by operational officers and, as a result, the remaining lifespan of the battery is relatively short.
“We are advised that it is now very likely that the training Taser’s battery is now inert and not able to be discharged.”
It is illegal for a member of the public to possess a Taser.
Police said the missing weapon was bright yellow and similar in size, shape and weight to a child’s toy gun.
The spokesman for West Yorkshire Police said: “It would be inappropriate at this time to be speculating about disciplinary matters over this incident until we have established the circumstances of the Taser’s disappearance. There may have been a genuine accident and there is no suggestion that there has been a break-in.”
Anyone with information about the Taser’s whereabouts should call police on 0845 6060606.
Earlier this week, burglars made off with radios and uniforms after breaking into a police station in Scotland.
Strathclyde Police said the stolen radios had been disabled and could not be used.