Twitter's employees celebrated their IPO (and instant millionaire statuses?) in style last night on their 9th floor rooftop, and we snapped this TMZ-esque shot amid blaring Lady Gaga songs and heat lamps. The floor doubles as an event space by night, but during the day it's a restaurant-quality dining facility for Twitter that seats 500 (we hear quail's on the menu--does that count as cannibalism?). Shorenstein's VP of leasing Jim Collins tells us the roof of the Art Deco building once functioned as a warehouse to store furniture, and that wood was repurposed and turned into paneling for the lobby downstairs.

We have the exclusive on a new tenant headed to the 1355 Market site. Sosh, which scours cities for unique activities to do (aka a hipster's dream), just signed for about 8,200 SF on the second floor. The personal concierge, built by Offline Labs, just raised a $10.1M round this summer led by VC heavyweight Khosla Ventures. Never in Jim's wildest dreams did he think tenants would pay over $50 per SF to sit in the Civic Center submarket (which had a 35% vacancy rate at the time of Shorenstein's purchase a few years ago). Twitter just exercised its option to take the fifth and sixth floors, and that rent will start up in the next 120 days (Twitter now leases approximately 75% of the site).

In its lease, Twitter negotiated putting an electronic Twitter feed on its facade but hasn't pursued that option yet. (An NYSE ticker could be appropriate now, too.) Now that 1355 Market is 97%-leased, Shorenstein is redirecting its focus to its project in the back: 1 TENth is a 1970s-era, 10-story building currently being redeveloped for delivery in the spring. He says there are "high prospects" to go in that building, which will be connected to 1355 via a landscaped plaza. Whether Twitter will spill into that site is unknown. That would mean Shorenstein's putting most of its (Twitter) eggs in one basket, but so far so good: shares hit a high of $50 in its first day of trading in New York.