* Sorrell quit on Saturday after investigation
* Two execs appointed joint COO as CEO hunt begins
* Departure comes at time of huge industry change
LONDON, April 16 (Reuters) - WPP, the world's biggest advertising company, will head into uncharted territory on Monday when it starts life without its founder Martin Sorrell, whose departure has left it rudderless at a time of swirling industry change.
The driving force behind 33 years of dealmaking and relentless expansion, Sorrell stepped down on Saturday after the board investigated an allegation of misconduct, saying that the disruption was putting too much strain on the company.
While WPP hunts for a new CEO, it has handed the helm to two executives, digital boss Mark Read and Andrew Scott, the chief operating officer of WPP Europe who oversaw acquisitions, making them joint chief operating officers.
The sudden departure of Sorrell, the face of the company since he founded it in 1985, has sparked questions as to whether the holding group can remain in its current form of employing 200,000 people in more than 400 companies across 112 countries.
"Sorrell's departure is negative considering ... how instrumental he has been in assembling the assets WPP has today," said Pivotal Research analyst Brian Wieser.
"Any executive filling Sorrell's shoes needs to orchestrate assets across the holding company and doing so is a challenge in a fragmented federation of businesses such as those which exist within WPP."
The 73-year-old's departure comes at a difficult time for the British company. In March it published its weakest results since the financial crisis as consumer goods groups such as Unilever and P&G cut spending and other customers jumped ship.
The whole industry is also battling the might of Google and Facebook, which dominate the online advertising market, and watching nervously as consultants such as Accenture move more aggressively into the sector.
The changing dynamics have meant the previous idea of building marketing groups up to offer advertising, branding, planning and research on a global scale - championed by Sorrell and followed by others - is now under threat as clients want more nimble relationships in a digital age.
Many are starting to ask if they can do things differently - creating their own content to place directly on online platforms or working with smaller ad groups.
With so much change in the industry, some analysts have questioned whether the group should seek a new CEO from outside who could look at it dispassionately.
Names already in the frame from the industry include Jerry Buhlmann, who runs the Dentsu Aegis network, and Adam Crozier who previously ran broadcaster ITV and Royal Mail.
From inside WPP Read, 51, is seen as the lead candidate.
While a common refrain heard about WPP is that no one knows the company like Sorrell, Read is the one man who comes close after he wrote to the WPP boss asking for a job in 1989.
From the company's office in Farm Street, Mayfair, he watched as Sorrell pulled off a string of takeovers before building his own profile by growing its digital operations.
He spent nearly 10 years on the WPP board, introducing him to investors, and is regarded by peers as a strategic thinker who can win corporate pitches to bring in work.
Scott, 49, is better known in the corporate world than the advertising community, having worked on the company's acquisition strategy but Sorrell welcomed both appointments.
"Mark will be responsible for clients, operating companies and people," a spokesman said. "Andrew will focus on financial and operational performance and implementing on-going reorganization of the group's portfolio."
They will "report to and be supported" by Roberto Quarta, the chairman who becomes executive chairman. Read has already contacted senior executives within WPP to offer to speak to clients and reassure them that work will continue as normal.
Whoever replaces Sorrell however will face longer-term questions as to whether a group that was built in his mould should remain intact after his departure. Already executives are predicting that bits will be sold off in a move that could once again become a model for the wider industry.
David Jones, the former CEO of WPP peer Havas and the founder of tech marketing group You and Mr Jones, predicted WPP would eventually end up missing Sorrell more than he would WPP.
"No one else can keep that company together the way he has been able to because he built it," he told Reuters. "It's the fall of an emperor and one that I think will not only take the empire down with him but will also have massive ramifications for that entire industry."
(Editing by David Evans)