Hoang, 36, was arrested Monday along with the head of his budget department, Tran Thi My Hanh.
Three other company executives are under house arrest.
The police said since May 2018 GFDI has been mobilizing deposits from individuals with the promise of paying high interest rates.
Hoang used "false information" to attract the deposits, saying the company would use the money to invest in projects with high returns.
The company published a variety of marketing materials to tout these projects and offered interest rates of up to 3.5% a month.
Hoang did not use the money for the promised purposes, and used money from later depositors to pay "interest" to earlier ones in what is known as a Ponzi scheme.
A total of 7,541 lenders deposited VND3.7 trillion with his company, the police have found.
Earlier this month Hoang informed the lenders that the company had become insolvent, and hundreds gathered at the company and demanded a refund.
Many were from other provinces, some were senior citizens who had deposited their life savings and there were even employees of Hoang who fell for the scheme.