Additionally, the brokerage firm found that younger investors are taking a greater interest in ETFs. Specifically, investors between the ages of 26 to 35 have 12.7% of their assets in ETFs, whereas investors between the ages of 66 to 75 only hold 6.2% of assets in ETFs.

The TD Ameritrade platform offers commission-free trading on over 100 ETFs.

For more information on the ETF fund flows, visit our ETF performance reports category.

Max Chen contributed to this article