Key Points:

A man pictured on a billboard removing electrical transformers worth $5000 probably knows by now he is about to get a visit from the police.

The man's photograph was plastered on several billboards around the city after he was snapped by a member of the public, stealing the transformers one Sunday in October.

"Who is this thief?" blared the billboards which also offered a $500 reward and included a telephone number.

Mark Venter, from OTW Advertising, the Parnell agency which owns the billboard, said his cellphone had been running hot with calls.

Sergeant Roy Simpson said several calls featured the same name and that person was being sought by police.

"One male has been mentioned more than once but other names have been put forward also and we have to investigate them," Mr Simpson said.

During the brazen theft the man wore a high-visibility, orange reflector vest from the Springhill Prison in North Waikato as he removed the transformers.

Mr Venter said the man was smart enough to know not to take the transformers at night when a time switch let power flow through to the lights illuminating the advertising on the billboard.

However, the wires were left lying on the roof near the billboard and became live when the switch tripped at night and for several hours during darkness arced and flashed around the roof.

"It was a huge danger and a massive fire risk and could have blown up the whole sign. He was a complete mongrel."

He said the billboard campaign to catch the man had produced an amazing community response.

Mr Venter said after having lost a few things to thieves, he was pleased in "knowing I had a photo and I could identify the theft with the bugger who stole it".