If blogs are over, tumblelogs never even got going. But that isn’t stopping Tumblr, short-form scrapbook blogging’s biggest exponent, from raising a $4.5 million second VC round. Beefing up, the outfit is adding former Time Warner (NYSE: TWX) technology SVP John Borthwick to its board and former CNET director John Maloney as president. The investment is led by Spark Capital and involves Union Square Ventures, who together led Tumblr’s $775,000 first round.

Part way between a blog and a Twitter microblog, a tumblelog is a space on which people publish short mixed-media posts. David Karp, who worked with Maloney at UrbanBaby, started Tumblr last year and has had just three staff; now it claims 15 million monthly uniques. In the release, he said the investment “presents some fascinating opportunities to grow the business and prove a sustainable model”. That will involve a premium model slated for Q1, though Karp also alluded to “a revenue strategy that leverages both Tumblr’s publishing platform and community” Advertising? Not yet, Karp tells AllThingsD, which values Tumblr at $15 million.