There's lots of online resources to find sex workers. What website you use, is probably determined by what country you're in. I've never heard of adultwork.com. There are even review sites where users can review - often in unnecessary & very creepy detail - their misadventures.
Twitter is also a very useful resource for sex workers and clients. It's a useful way for a worker to promote themselves and for potential clients to get a feel of the person before making a booking.
Even in a country where sex work is legal, I feel there is still quite a bit of opportunity to create a better online resource. Especially one that caters to the sex workers more. I feel a lot of websites are too client-centric and not as useful as they could be for client or worker.