I advertise on Craigslist when I need to. Although, most of the people who buy chicks already bought some from me in the past or were referred by past customers. I allow those people 1st opportunity to buy chicks before posting. Then when I post, I often end up getting another waitlist.
A lot depends on timing, and Craigslist can be silly. Sometimes it takes weeks or months of emails exchanges for a person to decide which kind of chicken to select. Other times, a person wants a chicken ASAP. If I take a day to respond, they may go out & buy chicks at a feed store. Price is also a huge variable. I ended up losing money with my chocolate cuckoo orps but can't hatch enough lav orps. Right now I have some very pretty Spitzhaubens which no one is buying. They're 5 weeks old and have been posted for sale for over 3 weeks! In April, I sold all 6 to the 1st person who saw them & had to turn away the next 3 interested parties. That ad was up for just a few hours.
I never tried Facebook, but have heard that it gets a lot of exposure. I'm in a suburban area, so roosters won't sell. People only want female chicks or adult hens. Since they end up going to small backyard flocks, most people want a pretty pet. What often happens is a family gets some feed store chicks & adds 1-2 of my orps. After several months to a year, I get another call asking for more. It's the common chicken math story. They see how stunning a real English Orp is compared to a hatchery Buff orp and want more in different colors. (Or their neighbors decide to get chickens & want an introduction to the "chicken lady.")