For David Sze and his colleagues at the venture capital firm Greylock Partners, the initial public offering for Facebook Inc. was a grand slam.
Sze, 46, a Boston native who grew up on Beacon Hill, led Greylock’s 2006 investment in the social media start-up. Back then, the firm put $12.5 million in what seemed like a risky deal. Today, that bet looks like every venture capitalist’s dream — a stake worth $1.5 billion.
On Friday, while hordes of small investors tried to buy into the much-anticipated IPO, Greylock was selling. The firm, with offices in Cambridge and in Menlo Park, Calif. — where Facebook is headquartered — sold about one-quarter of its 2 percent stake in the social network. And while outsiders lamented that the stock price didn’t soar, $38 a share added up to a heap of riches for Greylock, at about $330 million.
Sze wouldn’t ’fess up to uncorking bottles of champagne, but he did say the atmosphere has been festive the past two days. “My celebration was getting up at 5:30 in the morning and heading down to Facebook to be with the team while they rang the bell and opened up on Nasdaq,’’ he said. “There was a great sense of energy.”
Facebook employees stayed up all night for a “hackathon,” brainstorming new ideas.
And the night was fueled by the anticipation of ringing in the new stock symbol “FB.”
“It was very electric,’’ Sze said. “It was a real sense of achievement.”
It was also a huge win for an old-line Boston venture firm that’s become a player in hot social media and Internet companies, including LinkedIn, Dropbox, and Pandora.
Greylock was part of a group that invested last month in Instagram, the photo-sharing service that Facebook bought days later for $1 billion. The group put in $50 million and doubled its money almost instantly.
Sze said he’s looking forward: “What is next is always the question.”
Beth Healy can be reached at bhealy@globe.com.