Fraud

My colleague introduced me to his close friend who works with stock brokers and returns up to double the investment in a very short span of time 20-50 days. My colleague's younger brother and his friends had invested a lot of money and have been reaping benefits since last couple of months which I witnessed during a short visit to my colleague's younger brother's house. Hence I was convinced to invest and invested money. I was promised a return of 60% of the invested principal along with the principal in 3 weeks and money in my account by the 4th week. I was informed by my colleague at the end of the 3rd week that his friend is absconding with his wife and mother. Different investors are filing FIR consulting different lawyers. Please advice how to go about it to file a case.