OMAHA, Neb. (AP) — Billionaire Warren Buffett says he avoids buying into businesses like Facebook because it's too hard to estimate what they might be worth.

Buffett said on CNBC on Monday that he doesn't really have an opinion on Facebook and Google because it's hard to determine their value and how they will fare in the future.

Over the weekend, Buffett also told Berkshire Hathaway shareholders that initial public offerings are almost always bad investments. He says there is so much hype involved that IPOs won't be the most-attractive value.

Buffett said Monday that one of the worst mistakes investors make is buying or selling based on the day's headlines. He says investors should be looking for good businesses to buy and trying to determine how those companies will fare in 10 years.