They look like they are as small as gnats, or maybe smaller. Last winter I lost one of my hibiscus because of this problem. I have used Orthene on these, and it cut them down for a while, but they came back strong. Malathion gave me the same results. Either I am doing something wrong, or what I am using is wrong.
White flies are tenacious insects that can be very difficult to control.
For starters, move the hibiscus plant into your garage for winter protection, but not inside your home, or the insects will get on all of your other plants. Spray with a horticultural oil or Intercept. If using the oil, make sure you get thorough coverage to completely kill them out. Bright yellow sticky traps can also trap the insects, but this will take time. With diligence, you can control the problem, but it is not easy.