Facebook Inc. finds itself in the eye of a rapidly building legal storm over the disclosure of user data to political research firm Cambridge Analytica.  Lawsuits are piling up from users and investors. U.S. lawmakers are calling on Chief Executive Officer Mark Zuckerberg to testify before Congress next week.  The Federal Trade Commission is jumping into the fray, along with states and local government that are launching their probes or taking the company to court over its business practices...[P]laintiffs and government officials demand responses to subpoenas, which could potentially reveal more damaging information...Paul Grewal, a Facebook vice president and deputy general counsel, said the company is “committed to vigorously enforcing our policies to protect people’s information. We will take whatever steps are required to see that this happens.”...Users and investors have filed at least 18 lawsuits since last month’s revelations about Cambridge Analytica.  Beyond privacy violations, they are accusing Facebook of user agreement breaches, negligence, consumer fraud, unfair competition, securities fraud and racketeering.  Zuckerberg, Chief Operating Officer Sheryl Sandberg, and board members including Marc Andreessen and Peter Thiel face additional claims from shareholders for allegedly failing to uphold their fiduciary duties and wasting corporate assets...