Very reliable sources tell us that New York-based, social media-focused agency Mr. Youth, which also opened up shop in San Francisco a few months back, is narrowing down potential buyers and among those on the shortlist is LBi. Our sources say the valuation for Mr. Youth, which was founded by its CEO Matt Britton in 2002 (and signed private equity deals with Boston-based firms in early 2009) is somewhere in $50-75 million range. We hear a deal for Youth, an agency that has worked with the likes of Sony, Starbucks, HP and Macy’s in the past, will be completed by year’s end.