Linkin, who is described as a friendly boy, has epilepsy. He was due to have his medication at around 5pm.
Police said Linkin was carrying a green, MGP-brand scooter. The scooter has no wheels.
A Sunnyside Rd resident who lives near the Kukas said the police launched a major search this evening. "There's been a chopper bussing over with spotlights for quite a while, just doing circles over our house and shining a light down on this big subdivision development across the way from us. There was a cop car with a spotlight over there as well, circling for a while."
He hoped Linkin was found soon and said his thoughts were with the Kuka family. "It would be awful."
He said a local shopping mall was searched earlier.
A Police Northern Communications spokesman said at 10.03pm Linkin was still missing and the police were searching bushes, drains and other secluded areas.
Anyone who sees Linkin or knows where he is must call the police on 111 immediately.