The teenager's mother and two siblings were also at the scene, a popular surfing spot near Esperance.
It is the third fatal shark attack in Western Australia within 12 months.
The latest incident happened in the same area where a surfer lost his arms in a shark attack in 2014.
Neville Mansted, a professional fisherman, said he would not surf there again.
"That's twice now in the same spot. It could have been my son," he told The West Australian newspaper.
The beach will be closed for at least 48 hours while authorities investigate.