Activist investor Daniel Loeb announced over the weekend that his hedge fund, Third Point, has taken a $3.5 billion stake in the Swiss food conglomerate Nestle, and he wants some changes at the company. That may sound like a lot of money, but the investment represents just over a 1 percent stake in the company. It’s enough though to get the company’s attention. That’s because activist investors are looking to drive change, unlike a lot of “passive” investors, who just sell their stock if they don’t like how a company is run. How do activist investors work? Experts say if activists have a reputation for adding value and getting good returns, and if they have appealing ideas, they can win over other shareholders who will help them push for change.