Over a 100 rescuers from the fire brigade, police, and sea rescue services are still searching for the girl, who disappeared mid-afternoon after a piece of the cliff she was walking on broke off and fell into the sea.
A police spokesman said the spot where she disappeared is very difficult to reach from land.
Chunks of the chalk that makes up the coast of Germany's largest island often break off, and geologists have warned that this year's rainy summer has increased the danger of walking near the edge.
The largest slippage in nine years occurred in August this year, when a 100-metre long and 70-metre wide piece of the coastline slipped into the sea. Walks along the coast can be dangerous, but authorities have so far stopped short of blocking access to the entire 13 kilometre coastline.
Rising sea-levels have also been blamed for the land slippage. Geologist Ingolf Stodian says the Baltic has risen all of 28 centimetres in the past 200 years, leaving the cliff face exposed.