Tumblr Inc. Chief Executive Officer David Karp, a 26-year-old who started the company in 2007, signed a note announcing Yahoo! Inc.'s $1.1 billion acquisition with the closing, "F-ck yeah."

Beyond just expressing elation, Karp was making a statement that the New York-based company will retain its distinctive and irreverent character under a new owner. The phrase is common parlance at the social-media upstart, used in the titles of some of its most popular blogs. In its own statement on the deal, Yahoo echoed the idea of giving Karp and Tumblr a wide berth, saying it "promises not to screw it up."

"Our headquarters isn't moving. Our team isn't changing. Our road map isn't changing," Karp said. "Our mission — to empower creators to make their best work and get it in front of the audience they deserve — certainly isn't changing."