Eight incidents were reported to West Midlands Police in just one day – between Monday and Tuesday morning.
Catalytic converters were stolen in Tividale, Brierley Hill and Pedmore. And thieves tried to steal a further three catalytic converters in Quarry Bank, Halesowen and Wolverhampton – but were unsuccessful.
Officers also received a call about men with weapons attempting to steal cars in West Bromwich in the early hours of Tuesday morning.
A spokesman for West Midlands Police said: "We think the same group of people are responsible and we are doing everything we can to trace them.
"The suspects have weapons and could be dangerous. If you see them, please don’t confront them. Call us on 999 instead.
"If you have got any other information that could help our investigation, please let us know."
Catalytic converters are devices on the exhausts of cars that reduce toxic gases and pollutants. They contain precious metals making them a target for criminals.
The most commonly targeted vehicles are hybrid ones, as the catalytic converter is used less often and, as a result, the metals are not as corroded, making them more valuable.
Anyone with information, should call West Midlands Police on 101 quoting investigation number 20/564459/21.
Alternatively, call Crimestoppers anonymously on 0800 555111.