There isn’t a great way to do this online, really. The real trouble is standing out from the crowd, finding good clients, and establishing trust.
You could look for listings on Craigslist or whatever your local equivalent might be. Freelance websites have the market, but they also have the competition. To be successful you need to build a reputation and be able to deliver higher quality at a competitive rate. Depending on your location this can be very hard, especially if you live somewhere with a higher cost of living and you’re competing with people that have a lower cost of living and they can consistently undercut you.
The other way is to make yourself more visible online to people doing searches for web developers. You can grind away building online content that is SEO savvy and points to your freelance business, or you can stump up and buy some Google / Facebook / LinkedIn ads to get more eyeballs on your business.
But the online-only pathway to establishing a freelance Web business is going to be harder than being an in-person, live human being that can shake hands and laugh appropriately at potential clients’ jobs etc.
All that said, if you think you can compete with established freelancers in the freelance sites, then go for it. Plenty of people do it, so it must be making someone some money!