SAN FRANCISCO - Knight Ridder Inc.'s largest shareholder wants the nation's second-biggest newspaper publisher to seek a buyer, contending there are few other options left for a company that has been rapidly losing favor with investors as more advertising shifts to the Internet.

Private Capital Management LP, which owns a 19 percent stake in Knight Ridder, made the demand Tuesday in a letter addressed to the company's board.

PCM's letter reflects its frustration with a steep slide in Knight Ridder's stock. The shares have steadily declined from a 52-week high of $71.01 last November, trading at $52.42 less than two weeks ago — a 25 percent decline that wiped out $1.7 billion in stockholder wealth.

PCM's letter didn't identify what it would consider to be a fair price for Knight Ridder, but asserted that the company's own board already has determined the newspapers' break-up value exceed their current market value.