The inquiry is similar to one launched by prosecutors last year in Braunschweig, near VW's Wolfsburg headquarters, into current and former VW board members over whether they delayed the release of information about the cheating of diesel emissions tests.
The Stuttgart prosecutor's office declined to give details about its probe on Wednesday, but said it was in response to a complaint from markets regulator BaFin about current and former Porsche Automobil Holding SE board members Matthias Mueller, Hans Dieter Poetsch, Martin Winterkorn and Philipp von Hagen.
Porsche SE, which is headquartered in Stuttgart, controls 52.2 percent of VW's voting shares. Poetsch and Mueller are currently also chairman and CEO of VW respectively, while Winterkorn is a former CEO of VW. Von Hagen is responsible for investment management on Porsche SE's board.
A Porsche SE spokesman said the company had been in touch with Bafin, but had no knowledge of the Stuttgart prosecutors' probe.
VW and its current and former executives have repeatedly denied any market manipulation over the disclosure of its emissions test cheating.
BaFin said on Wednesday it had alerted Stuttgart prosecutors in summer 2016 about the potential market manipulation in the trading of Porsche SE shares, the same time that Braunschweig prosecutors launched their probe into VW officials.
(Reporting by Edward Taylor; Additional reporting by Andreas Kroner and Jan Schwartz; Editing by Arno Schuetze and Mark Potter)
(This story has not been edited by NDTV staff and is auto-generated from a syndicated feed.)
