Vianet Group shares plunged Friday after the real time monitoring systems provider announced half-year trading fell short of management expectations. Shares tumbled over 20% on Friday morning as the group said its results for the six months to March 31st this year missed targets. The company, which provides monitoring systems and data management to the leisure, vending, and forecourt services sectors, also estimates full-year profit before exceptional items and amortisation of around £3.2m, compared to £3.9m last year. Vianet said increased investment in the US, delays in new contracts and pressure in the leisure sector impacted performance. "It is obviously disappointing to be downgrading expectations," said Chief Executive, James Dickson."We have made good progress in a number of areas but have not been able to offset the effect of contract delays. The investment made in the US and recent contract wins in the UK means that the outlook for 2014 remains promising."He said actions have been taken to reduce costs across the group, particularly in its Fuel Solutions business which supplies management information to petrol operators via a web-based solution."It is against this backdrop and the continued strong cash generation that the board expects to maintain the dividend."The group expects to issue a total dividend of 5.7p per share.RD