Twitter stocks open today at $26 a share. The New York Stock Exchange has been buzzing or "tweeting" with the big news since 9 a.m. this morning. Macy's has a market capitalization of $17 billion dollars. The social network Twitter has a whopping $18 billion dollar market capitalization which is expected to increase in the new year. The last big social network to hit Wall Street was Facebook in May 2012.