Since its public debut, Facebook’s stock has dropped about 28 percent. As it tries to prove its IPO-day valuation of $100 billion, it will inevitably be under pressure to show investors that it’s willing to open up more of its platform – and, eventually, its data – to advertisers. For now, however, it seems that Facebook is roping off its contextual data about users from advertisers buying audiences through the new exchange. According to AdExchanger, the exchange partners and advertising clients will only be able to use their in-house data or information supplied by data partners, not Facebook data regarding user “likes” and other activity. In addition to holding back user data from advertisers, the social network said, users will still have the same control over ads they see on Facebook as they do now. According to estimates from research firm eMarketer, Facebook is on track to grow its ad revenues 60 percent this year to top$5 billion.