NEW YORK ( TheStreet) -- The Securities and Exchange Commission is investigating allegations that U.S. firms and individuals have joined with partners in China to steal billions of dollars from American investors through stock fraud, according to people familiar with the probe.Individuals with direct knowledge of the investigation say that the SEC is focusing on stock promoters, investment bankers, auditors and law firms that have been active in recruiting Chinese companies to U.S. stock exchanges and raising capital for those companies by selling new shares. On Monday, the SEC made an example of an auditing firm that it said had failed to protect U.S. investors from overstatement of revenue by a Chinese firm. The commission said it had reached a settlement with the firm -- Moore Stephens Wurth Frazer & Torbet -- and with Kelly Dean Yamagata, a partner. As part of the settlement, the firm will be temporarily barred from accepting new auditing assignments in China and will pay $129,500. The case relates to audits the firm did for China Energy Savings Technology, a China-based company that has been the focus of a series of SEC fraud complaints since 2006.