Facebook Inc.

[Big Toe]

My take is that Google and Facebook are at different stages of growth when they did their IPO.
Granted google had high valuations during IPO but they were small in absolute terms and they had much more space to grow.
Facebook on the other hand, is already having a few hundred million users before its IPO, we do not know how much bigger they can grow, my guess is, maybe not a lot more.

Also, there isn't a clear revenue stream. Advertising, yes, but is it as effective as search engine ads? I dont think so.
Google knows what you are looking for and will present the ads/search results according to your input.
Facebook will have a harder time trying do likewise. Not impossible but much harder.
BUt they will have more input/information to work on if they can figure out how.
If they are able to do that, advertisers will come flocking in and it may well become a more personal platform for advertisers.

Never easy to figure out these tech companies.
That's why Buffett bought See's candy sometime ago. Sweets, easy to understand.