We did run some FB ads and we also did some promoted posts - the latter were more effective than the former. I was pretty pumped about the potential to do FB advertising because of their demographic targeting capabilities we could specifically target women who were engaged for example. Sadly, they didn't do as well as I had expected.
We worked hard to max out our city (Calgary) first because it was easier to saturate a smaller market - then we spread out geographically organically after that. Definitely focused a lot on our personal networks, asking people to share our stuff occasionally - especially when we had something more broadly appealing.
Doing what you can to support a cause or charity is a big boon - not only does it do good, but it is way easier to get attention and help from people (in the form of sharing & liking, etc) when it is about a good cause rather than just self promotion. For example, a wedding dress shop burned down in Vancouver and a bunch of brides were going to be stuck without a dress for their weddings - so we set up a page where people could donate their dresses - then we promoted that, and lots of people were willing to share and spread the word, and then, of course, people went to the site and checked it out. We ended up transitioning that into a thing we called "Can't Buy Me Love" - which lets people donate their wedding items to brides who can't afford a big fancy wedding. So, keep your eyes open for ways to get on board helping a good cause. Perhaps you could do something related to fashion in some way? Maybe something to do with clothing for the needy?
We did a lot to reach out to other wedding vendors (photographers, hair salons, dress makers, etc) - sharing their stuff to our audience and asking them to do the same - this expanded our reach a lot.
We also joined a bunch of wedding groups on FB and did our best to promote our site there - it was helpful because it is free for brides & wives to use, so that opened a lot of doors.
Pinterest is a good medium, would be for you too - we set up our site so that every image that people post of their stuff for sale has a Pin-It button on it, so items get pinned frequently. We also created our own Pinterest profile and followed a bunch of wedding folks and repinned their stuff. We don't get as much traction on Pinterest as I thought we would - but partially I think it is because FB was working so well that we just focused our energies there. I think you could do really well on Pinterest with this since it is so visual and fashion content kills there.
Good luck!! Definitely keep us posted.