Pinterest may be looking to raise another round at a valuation as high as $2.5 billion, sources tell The Wall Street Journal. The site has seen huge growth in the last year with 28 million unique monthly visitors in December, up from 7.5 million the same time in 2011. The photo sharing site’s last round occurred in May of 2012, when it raised $100 million in a round led by Rakuten. [Source: The Wall Street Journal]