Yes, Facebook stock is struggling and it may struggle lots more as the shackles are taken off company insiders, which will allow them to sell more into the market in the coming months. But Facebook is real. It is not a vendor of vaporware like so many of those dot.com companies that never earned a penny but burned through cash faster than Mark Zuckerberg could burn through old friends.
Facebook is learning that what people like to chat about when they should be working isn't a very effective way to match ads to eyeballs. LinkedIn on the other hand has a very specific type of advertising structure, and one that works very well: job postings. Is there an ad people want to see more than one promising a better career?