Pinterest and Uber, two of the hottest startups, are seeking a fresh cash injection to fund their expansion. Pinterest, the online scrapbooking site, is looking to raise an additional $200 million in venture funding from its pool of investors the likes of Fidelity and Valiant Capital. With this latest round, Pinterest's valuation could be as much as $5 billion. In 2013, the company was valued at around $3.8 billion. On-demand taxi service Uber is also reportedly in talks with private equity firms. Its latest cash-raising activities could push its total worth to $10 billion. In 2013, Uber was valued at just $3.5 billion. Keris Lahiff reports from Wall Street.