TUI AG shareholder Fredriksen to sell 15.7 pct stake

* Fredriksen vehicle to offer 39.7 mln shares in placing

* Offer price to be determined via book build

* TUI AG (Xetra: TUI1.DE - news) shares up 35 pct since Fredriksen increased stake

FRANKFURT, Feb 19 (Reuters) - TUI AG shareholder and Norwegian shipping magnate John Fredriksen will sell a 15.7 percent stake in the German travel and tourism group, benefiting from a rise in the price of its shares.

Fredriksen increased his stake in TUI AG to over 20 percent and simultaneously sold his stake in the group's TUI Travel (LSE: TT.L - news) unit in November. At the time, his aide said the move meant Fredriksen had strengthened his influence should he decide to renew efforts to merge the two companies.

Since he increased his stake in November, TUI AG shares have risen by 35 percent as a turnaround took effect and the announcement of a first dividend since 2007 attracted investors.

Fredriksen's vehicle Monteray Enterprises will sell 39.7 million ordinary shares, via a placing to institutional investors, bookrunner Goldman Sachs (NYSE: GS-PB - news) said in a statement.

At Wednesday's close of 13.75 euros, the stake was worth 546 million euros. Fredriksen spent 83 million euros on increasing his stake in November at an average share price of 10.37 euros.

The price of the placing will be determined via an accelerated bookbuilding process to start immediately.

Shares in TUI AG dropped 2.5 percent in Frankfurt late trade .

The sale will leave Fredriksen, who was the group's second largest shareholder, with a 4.4 percent stake in TUI AG.