In his last job, stock market analyst Santosh Rao regularly met with executives from the public telecom companies he wrote reports about. In his current job, Mr. Rao can barely even get his phone calls returned.

Mr. Rao is one of a small but growing group of private tech research analysts who publish reports about venture-backed companies for potential investors. Several, including Mr. Rao, are former public equity analysts. They’re attempting to transplant the Wall Street research model for public companies to private tech investments—using the reports to help drive more stock trading, just as the public market firms do.