Before last year, Ed Medley had never invested in commercial real estate. Now, he's a part-owner of shopping malls, mobile-home parks and apartment buildings from Los Angeles to Tennessee.

Dr. Medley's springboard into real-estate investing was supplied by a process known as crowdfunding—the sale of shares in a venture, in this case real-estate projects, to hundreds or even thousands of individual investors. Dr. Medley, a consulting engineer and geologist in San Mateo, Calif., has invested in 15 properties, with a minimum...