When it comes to raising money on the Internet, the biggest buzz is generated by fan-financed projects such as "Veronica Mars," whose producers raised more than $5 million to make a movie based on the canceled cult television series.

But for investors looking for a return on their capital—"Veronica Mars" backers got T-shirts and movie posters—it is the prosaic property market that has been grabbing the spotlight.

Dozens of crowdfunding sites now offer individuals the chance to invest in everything from single-family fixer-uppers to ground-up real-estate developments and even distressed mortgages, sometimes for as little as $100. Many of the new platforms were launched in response to the Jumpstart Our Business Startups Act of 2012, which eased restrictions on fundraising by small companies, and have been operating for less than a year.

But already they have raised more than $135 million in debt and equity for real-estate deals, according to Wall Street Journal calculations.

Real estate is proving particularly popular largely because it is a tangible asset that people can look at and even visit. It is easier to understand and value than many technology startups, which were expected to be a primary beneficiary of the JOBS Act.