Overseas associates of a man who took off with his 11-year-old stepson are working with police, who are still trying to track him down.

John Beckenridge abducted Mike Zhao-Beckenridge from his Invercargill school in March 2015.

The pair camped in various places around the Catlins, before Beckenridge's dark blue four-wheel-drive went over a cliff near Curio Bay.

It took police six weeks to retrieve the wreckage - and there were no bodies inside.

The pair haven't been seen since.

Police say the inquiry is still live and some of Beckenridge's overseas associates are helping with the investigation.