Quick, Tweet it! Twitter announced Thursday that it has filed an S-1 with the SEC and is becoming public. The official confirmation read: "We've confidentially submitted an S-1 to the SEC for a planned IPO. This Tweet does not constitute an offer of any securities for sale." Twitter is expected to go public at a value between $15 and $20 billion. To compare: Facebook’s IPO valued the company at around $100 billion on the day it became public.