By Neil Parmar Social enterprises are getting a hard lesson in the realities of doing business.In recent years, more startups have appeared that aim to do traditional nonprofit jobs—such as training the homeless or providing services for the sick—while trying to make money. They think that going for-profit allows them to compete more aggressively for talent, shake off the control of big donors and move more nimbly than traditional charities.But as these small ventures try to scale up, they're having a tough time landing investment capital to fund their growth, experts and entrepreneurs say.Nearly 80% of social enterprises in the U.S. said they needed more funding to stimulate the growth of their businesses, according to a survey published in 2010 from Community Wealth Partners, the Social Enterprise Alliance and Duke University. Even though these companies have gained more interest among individual investors and philanthropists over the past 10 years, "it's still tough to raise money," says Jeffrey Bradach, managing partner of Bridgespan Group.In part, that's because there are lots of social ventures chasing the same dollars. But it also marks differences between the missions and methods of these outfits and traditional businesses. By and large, these companies don't keep the sorts of statistics investors and lenders want. While they track basics like revenue, they often don't come up with revenue projections and impact numbers, such as the number of students an education nonprofit helped and how much those students' grades improved. So, it's hard for investors to see how well a company can scale up while boosting revenue and profit margins, experts say.Then there's the simple fact that many companies earn only a "modest" profit, so they're "not going to have an appeal to a venture-capital firm or an investor that wants a higher return," says Amy Celep, chief executive of Community Wealth Partners.To be sure, some social enterprises haven't had as tough a time. Sectors like renewable energy, food security and clean water have gotten a lot of media attention, which makes it easier to secure capital.For those that are still struggling, one increasingly popular solution is an online campaign on peer-to-peer funding sites like StartSomeGood.com or Causes.com. The tactic has allowed some companies to validate demand for their product or service, which experts say could convince some skeptical banks or venture capitalists to turn on the money tap.Emzingo Group LLC, for one, is a New York-based company that trains business leaders to tackle social problems. It attracted $50,000 through a crowdfunding campaign last year, and it's now seeking around $3 million to expand its program from roughly 50 fellows in South Africa and Peru to about 300 fellows in up to five sites by 2016. The success of Emzingo's campaign recently helped convince a Spanish impact-investment fund to provide more than $250,000 in a so-called patient capital loan, which doesn't have to be repaid for a long period. "It was a stepping stone," says Pablo Esteves, Emzingo's director for advisory services. Mr. Parmar is managing editor for WSJ.Money magazine. He can be reached at neil.parmar@dowjones.com.