The board has decided to conduct a formal sale process in order to identify appropriate potential partners for the company, or major strategic investors, PLUS said in a statement on Friday.
The board believes that it is in the best interests of the company to seek a partner which will help it achieve the scale and reach required to maximise value to stakeholders.
PLUS, which also operates the PLUS DX derivatives exchange, grew out of Ofex, an exchange for British small cap stocks that required less regulation than the London Stock Exchange or AIM.
The company reported a loss of 5.8 million pounds on revenue of 3 million pounds in 2010, its sixth consecutive loss-making year.
The sale is being handled by corporate finance advisory firm Wyvern Partners.
Plus Market shares were down 11 percent at one pence by 1550 GMT.
(Reporting by Myles Neligan; Editing by David Holmes)