UPDATE 2-CBS buys outdoor ad company for $110 mln

(Adds stock price movement, background)

NEW YORK, April 24 (Reuters) - CBS Corp (CBS.N) said on Thursday it bought International Outdoor Advertising Group (IOA), which operates in South America, for $100 million to bolster the broadcaster's fastest growing business segment.

The cash purchase complements CBS's billboard businesses in Mexico and Spain, CBS Chief Executive Leslie Moonves said in a statement. It also gives the company an entry into Argentina, Brazil, Chile and Uruguay, which comprise more than two-thirds of South America's population.

Shares of the New York-based owner of the CBS Television Network and Showtime cable TV network, which rose as much as 3 percent in early trading on Thursday, have been among the hardest hit among big U.S. media conglomerates.

Investors fear the company's higher exposure to traditional TV and radio advertising makes it more vulnerable in a deteriorating economy.

CBS is betting the deal will help sustain momentum in its fastest growing division. In 2007, revenue at CBS outdoor advertising business rose close to 10 percent and profit rose more than 15 percent.

IOA Chief Executive Jack Sabaj will continue to run the business, reporting to CBS Outdoor International's chief development officer, Antonio Alonso.

Moonves said in March he would not be surprised if about 20 percent of CBS's business was generated outside the United States in three to five years.

The company now gets about 10 percent of its revenue from non-U.S. operations, less than many of its big media peers.

CBS shares rose 31 cents to $21.70 on the New York Stock Exchange. (Reporting by Robert MacMillan and Kenneth Li)