I work for a medium sized public company (500 people), that went public about 5 years ago. After going public we had a CEO that was decent, but didn't know how to run a company to make it profitable. After 1.5 years of missing earnings we got a new CEO and our stock is 10x the value it was back then.
If Zuckerburg is still playing a part in engineering, he should be the CTO of the company, not the CEO. Having a business minded person person holding the reigns of a company can help the shareholders, otherwise the stock price will have a good chance to continue its descent.