Shares in Seven West Media have plunged by more than 16 per cent after it cut its earnings forecasts due to ongoing weakness in advertising markets.

Seven West shares were down 61 cents, or 16.2 per cent, at $3.16 at 1018 AEST.

The company owns the Seven TV network, publisher Pacific Magazines, Yahoo!7, The West Australian newspaper, regional mastheads and radio stations.

It issued a statement after trading closed on Tuesday to inform the market an expected improvement in the advertisement market had not eventuated.

As a result, its earnings forecast for the year to June 30 has been lowered to between $460 million and $470 million.

Seven West reported earnings before interest and tax (EBIT) of $309.7 million for the first half of the 2011/12 financial year.

Shares in other media companies did not fall as sharply.

Fellow broadcaster Ten was steady at 81.5 cents, and Southern Cross Media was down five cents at $1.32.

Fairfax was down two cents to 70 cents, News Corp was up one cent at $18.89, and APN News and Media shares were half a cent lower at 81.5 cents.