The lawyer for the family of a Sydney teenager believed to be fighting in Iraq says Australian Federal Police (AFP) could have stopped the boy en route to the conflict.

Abdullah Elmir, 17, went missing from his home at Bankstown in Sydney more than a week ago.

Zali Burrows, a solicitor representing the family, says the teen called his mother days later to say he was in Turkey about to "cross the border".

She says his mother took that to mean Abdullah, a "typical Aussie teenager" who likes fishing and outdoor sports, was heading to Iraq.

"You can understand, she's devastated. She's thinking the worst," Ms Burrows said.

"She doesn't know exactly where he's gone or if he's in a training camp."

Ms Burrows says the family fear his decision was triggered by an online campaign.

"He's been influenced by something on the internet," she said.

"Unfortunately, they can come across these videos asking them to come over and help."

Ms Burrows is questioning how Abdullah and a 16-year-old boy he was travelling with were not stopped by Federal Police, who she says was monitoring Abdullah.

"He's obviously under surveillance ... he has been for quite some time," she said.

"We know this because certain people around the family have been approached by ASIO officers showing photos of him.

"If they were watching this kid, they knew he was planning to go overseas."

She says the pair took an indirect route, travelling from Sydney to Perth and onto Malaysia and Thailand before finally reaching Turkey, providing several points where police could have picked up the teens.

"Why did they let him slip through?" she asked.

"Is it because they want to use him as, let's say, a sacrificial lamb, a tracking device, as to further their intelligence in their investigation overseas?

"[The family] know the Government knows where their son is ... this is really a cry for help, a plea for help."

Attorney-General's Department 'unaware' of Abdullah's plans

Federal Police have referred inquiries about the case to the Attorney-General's Department, which says neither organisation knew of Abdullah's intentions.

The department says it will not confirm individual cases, but remains concerned about Australians, particularly young people, travelling to conflict zones.

"The Australian Government has been warning of the dangers of travelling to Syria and the surrounding region since 2013," a spokesperson for the Attorney-General said.

"It is of particular concern that youths are putting themselves at risk of kidnapping, serious injury or death, and potentially taking part in the conflicts taking place in Syria and Iraq.

"However, individuals make, and are responsible for, their own travel decisions. The Government only seeks to prevent a person from travelling overseas if they are believed to be seeking to engage in activities prejudicial to national security.

"The Government is not responsible for monitoring the activities of youths. Parents and the broader community share the responsibility to partner with the Government in educating their children about the risks associated with travelling to Syria and the region and ensuring they do not put themselves or others in danger.

"In this instance, neither the AFP or any other government agency was aware of the child's plans to depart Australia for Syria."

There is no consular assistance available in Iraq due to the volatile situation.