Fifteen-year-old Troy Drummond and his brother Jay, 14, were given motorbikes by their parents and planned to start competing in enduro races this year with a Dandenong club.

But two weeks ago thieves took the bikes, which cost $12,000, from the family garage in Margate Avenue, leaving the brothers with two small bikes that they have outgrown and are not suitable for enduro racing.

The boys' mother Paula Drummond said: "One man has phoned me saying he heard noisy motorbikes in a lane between his house and Bruce Park at 3.19am.

"He knew the time because his dog had been disturbed and started barking."

Mrs Drummond, who is offering $1000 to get the bikes back, said the man was one of many people who had responded to leaflets she had distributed in letterboxes throughout the neighbourhood in a bid to find the thieves.

The bikes stolen on Thursday, January 28 are a 2007 yellow and black RMZ 250 Suzuki decorated with a motorsport.com sticker kit and a red and white freestyle CRF250R Honda 2009, which carried the number 58 and was also sporting a sticker kit.

The Suzuki cost $5500 and the Honda $6500.

Anyone who can help find the bikes can phone Paula Drummond on 0421994338 or Frankston police 97845555.