100 in three years is more reasonable then next year as may people are touting. It is still a real long ways away and there is a lot that FB would have to do to get there. It would also be one of the fastest rise for a 70 billion dollar stock to to triple in three years.
Here is the thing and that is it would still be a very nice gain if FB got to $50 in three years (which still would not be assured) but the target is more like what you might see in other comparable hyper growth stocks. The big risk is the same risk there is in all growth and that is there are no guaranties because the path there is blind.
The best rule for investing that I can give is to not create targets but to invest while a stock is viable and running and to spread money across multiple sectors to avert losing large amounts in a portfolio due to negative performance.
FB is a good stock. 100 in three years is pretty optimistic. I do hope it gets there for you.