Tonga Power says it has spent more than 10,000 US dollars repairing power poles and transformers on Tongatapu.
The damage has caused power cuts.
Radio Tonga reports that the insulators at the top of electricity poles have been damaged by teenagers using slingshots and stones.
And electricity wires have had to be replaced at a cost of nearly 5,000 US dollars.
The company's Chief Executive, John Van Brink, says the concern is not just cost but safety.