NYC-based CDN Panther Express has raised a $15.75 million second round led by Index Ventures, along with Gold Hill Capital and previous backer Greylock. The company’s first round of $6 million came in 2006, for a total raise of at least $21.75 million. Helmed by ex-DoubleClick CEO Kevin Ryan, Panther Express firm claims 200 US customers and another 50 in Europe. Customers operate in areas like video, audio, ad serving, gaming and social networking. Funding will go towards expanding internationally and building out its infrastructure. Releasehttp://finance.paidcontent.org/paidcontent?GUID=4733146&Page=MediaViewer&ChannelID=3197.