Ashton Kutcher is perhaps the most vocal celebrity investor. The actor, who rose to prominence on That 70s Show, has made his passion for tech clear. He was one of the early proponents of Twitter and even filmed a movie, starring as Apple co-founder Steve Jobs. And he's participated in dozens of venture rounds. Well-known start-ups such as Path, Airbnb, Flipboard and Fab have all made the Kutcher investment list. He was also on the investment team for news summarizer, Summly, which sold to Yahoo for $30 million. Investors who've worked with Kutcher offer praise. Ben Lerer, managing director at Lerer Ventures, said: "In my dealings with Ashton, he's been very thoughtful about the companies and isn't just investing because he's got money to burn." Lerer said Kutcher is "a really smart guy who loves technology and understands how the world is changing." Metamorphic's Krall says people such as Kutcher "really add value and are not necessarily just brought on to increase word of mouth by who they are." Still, not all of his investments are resounding success stories. Local service provider Zaarly is looking to drastically change its business model. And Sean Parker-backed video chat service Airtime has struggled to attract a strong user base.