First of all, increasing your exposure with a tanking stock is an awful plan to make money. If FB has been trading for years and you knew its patterns well, then you can identify support levels and buy the dips - but Facebook is two weeks old and going over like a fart in church, and you want to buy more on the way down? Ever hear of trading out of a bad position?
I won't tell you what to do, but a market pro might have a very simple suggestion and say "cut your losses".
If I were looking for short term gains I would agree with you. As I have mentioned earlier this is a long term bet for me. I dont believe in following the trends. If everyone says to run away, sell and cut your losses, then I will turn around and buy as much as I can. And this is one of those cases where I think it makes sense to go against the grain. This isnt advice or anything other than an educated guess.
I have already set the reminder to bump this thread in 2 years. We will see what happens. If I am wrong I will be the first to admit it.