Authorities have confirmed a code word was at the centre of a miscommunication that led to the family of teen bushwalker, Lily Hooper, initially being informed she'd been found alive.

Nearly 100 soldiers have joined the search for missing Sydney bushwalker Lily Hooper.

Lily Hooper was found on Thursday morning, more than a week after she went missing in dense bushland.

Lily Hooper had been missing in bush near Sydney for eight days.