As a modern jewelry retailer, you’re probably already utilizing the A-list social media sites—Facebook, Twitter, Pinterest, LinkedIn, and Instagram—to promote your store. But if luring millennials is a priority, consider establishing a presence on one (or more) of the many newer social networks.There’s certainly good reason to market on, say, Facebook; that’s where your 40- to 60-year-old clients are hanging out. But Twitter trumped it in popularity among teens in 2013, according to Piper Jaffray market research. (Only 23 percent of those polled said Facebook was their favorite network, down from 42 percent the year before.)Where are millennials getting social? Where their parents and teachers aren’t, of course. Here’s a primer on the networks capturing their attention:TumblrThe blogging platform Tumblr, which was acquired by Yahoo! in mid-2013, also allows users to post co