Call for bushwalkers in search effort

Volunteer bushwalkers are expected to bolster the search effort for a Sydney man who hasn't been seen in over 10 days.

Sevak Simonian was last seen when he left his Sydney northern beaches home on October 20 to go bushwalking.

His car was found Kanangara Boyd National Park at Oberon last Friday.

Emergency services have spent the past week scouring the dense national park terrain but have found no sign of the 21-year-old.

The NSW National Parks Association appealed to its members to join police with the search effort and meet at the park on Friday morning.

It comes after adventurer Dick Smith reportedly used his helicopter to search above the national park for Mr Simonian this week.

Mr Simonian's family are confident in his bush-surviving skills but admit the wait has been agonising

"I don't know what to do," mother Rosa told ABC Radio on Thursday.

"I can't go on without him."

Any visitors to the park that have sighted Mr Simonian are urged to contact police.