Abby Sunderland's yacht was spotted by an aerial search team in the southern Indian Ocean, midway between Australia and Africa.
Three ships are on their way to pick her up - the first is expected to be with her in 24 hours.
The teenager's family lost contact with her for some 20 hours, after she said she was caught in 30ft (9m) high waves.
Shortly after contact was lost, at around 1300 GMT on Thursday, the yacht's emergency beacons were manually activated, more than 3,220km (2,000 miles) from the coasts of both Africa and Australia.
A Qantas Airbus A330 search plane - scrambled from Perth early on Friday - spotted the teenager's boat, called Wild Eyes, and made contact with her.