You have to be alreadyy branded, perhaps even before facebook came out. Hard to build up the popularity of startups on facebook.
You can get 100k fans by having a solid marketable brand, and then initiating a campaign to slowly build your fan base. you can start building by buy facebook fans slowly until you have a solid fan base.
Combining your Facebook Campaign with email marketing is the most effective way to grow your fans. Add a Facebook Advert that's targeted to your audience and you've got a winning recipe. However these will all need to be very well managed and strategised. You also require a well managed database and if you lack this you should start off with a database acquisition campaign.
How have you accrued that amount of fans? Share your tips, guys. As I am about to start using FB to attract more pople to my site. Will be happy to hear your stories