Group 1 - A significant drop in stock prices of several Chinese micro-cap stocks listed in the US has resulted in investors losing billions of dollars, raising concerns about a potential "pump and dump" scheme [1] - Seven specific stocks, including Concorde International (CIGL.US) and Austin Technology (OST.US), have seen declines exceeding 80% in recent trading days, leading to a total market value loss of $3.7 billion [1] - Prior to the sharp declines, these stocks had experienced substantial increases and were promoted on social media platforms like WhatsApp [1] Group 2 - Brain Regen Technologies (RGC.US) has seen its stock price increase nearly 10,000% this year, with no current evidence linking the company to stock price fluctuations [2] - The FBI reported a 300% increase in complaints related to "pump and dump" stock fraud over the past year, indicating a rise in investor victimization [2] - Fraud groups are reportedly using social media ads and "investment club" promotions to lure investors, sometimes impersonating legitimate brokerage firms or well-known stock analysts [2]