Legal Question in Business Law in California

Usually not. Can you imagine, as a shareholder-creditor of, say, IBM or General Motors, trying to collect your debt in equal (or any other) proportions from 10 million constantly-changing shareholders? It is a basic principle of corporate law that the corporation is not its shareholders; that they are separate and distinct and that the shareholders are not liable for corporate debts.

However, there is a special principle that is sometimes applied to "flaky" corporations that are not organized, capitalized and operated in compliance with normal corporate standards and rules. When, for example, three or four guys form a corporation, but then fail to observe its bylaws, don't put in much capital, don't have board meetings or keep minutes, commingle corporate assets with personal assets, and so forth; in effect when they operate with almost complete disregard for corporate rules and procedures -- then it MIGHT be possible to convince a court to disregard the corporate entity and sue the individual stockholders, officers, directors, or whatever the bozos running the business call themselves.

This process is sometimes called "piercing the corporate veil" or by similar slangy expressions. More formally, the term "alter ego" is often used.

There are a lot of cases worth looking at, or you might go to a law library (there's one in every county) and ask the librarian to help you find a treatise on "alter ego" or "veil piercing." Friedman on Corporations is one I use. A good case to look up as a starting point is Sonora Diamond Corp. v. Superior Court of Tuolomne County (2000) 83 Cal.App.4th 523.

Easy answer: shareholders are not liable for the debts of the company, other than by reduction in the value of their shares if the company suffers in the Stock Market.