ACT Policing has published images of two men they believe might be involved with the theft of two vehicles in the ACT and one in NSW this week.

They are seeking witnesses and information about these incidents.

A blue Hyundai i30 was reported stolen from the car park of a gym in Conder between 8.20pm and 9pm on Tuesday.

The same day, a similar theft occurred at a gym in the Googong area, when a white ute was stolen from a gym car park late in the afternoon.

A subsequent theft occurred on Wednesday, December 16, when a silver Toyota Prado was reported stolen from a Coombs Gym between 11.40am and 12.30pm. The car was later found in Duffy.

Police believe that in the case of all three thefts offenders entered the gym, stole car keys and fled in the vehicle while the owners worked out.

It is not known if the offenders were members of the gyms they targeted.

Officer in charge of Tuggeranong Station Detective Acting Inspector Simon Coady urged people to secure their valuables when they visited the gym.

"Unfortunately if your keys are out in the open unattended it makes it easy for an offender to steal your vehicle while you are preoccupied with your workout," Detective Acting Inspector Coady said.

"If there are lockers available, be sure to secure your valuables and never loan your gym pass to anyone else.

"If you see someone entering the gym without a pass or anyone who shouldn't be there, make sure you let management know."

Anyone who recognises the men or has information about these car thefts is asked to contact Crime Stoppers on 1800 333 000, or via the Crime Stoppers ACT website quoting reference number 6695411. Information can be provided anonymously.