I've tried backpages, craig's list, and a slew more and the results have been mixed. I guess it's like anything else, you have to have a engaging title and short but great copy. Even then this doesn't guarantee success. I have found that classified ads can be a crap shoot. Hope it works well for you, take care.
I never tried promoting my FB page on classified ads, but I would never consider doing so. I believe the means is not appropriate with the ends you want to achieve.
Free / paid? What classifieds are you thinking about? If you're considering the big dogs some of them have rather stringent rules and your FB ads may not stick unless you pay.
I'm trying free advertising methods until I gain a large enough following and then I will monetize the traffic and start doing paid advertising to get even more followers.
I won't consider doing classified ads because I know that's not the best way to reach my market. How about yours? What's your niche, and why do you consider this medium?
I'm in the music niche. I have a fairly young demographic which uses online classifieds so I will test it out.