Blackstone Group has hired away a General Atlantic executive to launch a business that will invest in fast-growing companies.

Jon Korngold, an 18-year veteran of General Atlantic who served on the private equity firm’s management committee and led its investments in financial services and health care, will lead Blackstone’s new platform. The unit will take stakes in companies in a phase of development falling between early-stage venture-capital investments and more mature traditional buyout targets.