The parts are attached to vehicle exhausts and contain precious metals used to reduce the amount of dangerous gases that are pumped into the air.
North Wales Police say there is “an emerging series of such robberies” in their territory and in neighboring force areas of Cheshire and West Mercia, which includes Shropshire.
Since January this year, 15 incidents have been recorded in the districts of Flintshire, Wrexham and Denbighshire.
The most recent report officers dealt with is believed to have occurred overnight on Sunday at an address on Whalley’s Way in the village of Acrefair, near Llangollen.
Catalytic converters are often targeted by thieves and police say they can be removed in less than a minute.
Chief Inspector Gavin Gilmore said: “We are currently seeing an increase in the theft of catalytic converters in our area of strength.
“Precious metals such as rhodium, platinum and palladium are used in catalytic converters and we know they are sought after by thieves.
“The price of these metals has risen sharply in recent years and has led to an increase in theft crimes.
“Several thefts of converters have involved Japanese vehicles, in particular the Honda Jazz car model.
“While we urge drivers of this model of vehicle to be extra careful, we are warning all vehicle owners to be aware of the threat posed by opportunistic thieves.
“The most recent report we dealt with is believed to have been on the night of Sunday April 24 at an address on Whalley’s Way, Acrefair.
“We are appealing to witnesses to this incident and anyone with CCTV/dashcam footage to report via 101, quoting incident number B058050.
“I also urge anyone who witnesses suspicious behavior around parked vehicles to act quickly and report it to us.”
Officers investigating these incidents believe a recent spate of thefts from parked vehicles may be linked to the same offenders.
Although catalytic converter thefts are increasing nationwide, there are steps you can take to protect your vehicle.
To ensure the safety of your catalytic converter, you can ask your car dealer for advice on locks or guards approved by the vehicle manufacturer and tested to Sold Secure Gold.
Otherwise, try to ensure your vehicle is parked in a garage overnight or, if you have a utility vehicle, park it in a secure enclosure.
If this is not possible, park in a well-lit, unobstructed area and try to park in such a way that the converter is not easily accessible by potential thieves.
Vehicles located above the road are particularly vulnerable.
You should also save your converter and mark it with a forensic marker, which will make it harder for thieves to get rid of it.
If you have been a victim of this type of theft, you can report the incidents to the police online.