Shares plunged 21% to 237p in morning trading.
The company ended negotiations with rivals Starwood Capital, TDR Capital and Terra Firm, which were approaching the August 7 deadline to make an offer.
"After extensive discussions exploring the interest shown by multiple parties over recent months, the board unanimously believes that none of the interested parties is currently capable of delivering an executable transaction at a recommendable price," IWG said.
"The board remains confident in the long-term value of and opportunities for IWG.”
The group last month won an extension from the Takeover Panel to allow more time for the three suitors to make a firm offer.
Previous approaches for IWG
IWG received a joint approach from Canadian bidders Onex Corp and Brookfield Asset Management in December but the talks fell apart in February. In July, real estate investor Prime Opportunities pulled out of the race to buy IWG after its offer was rejected in May.
"If you consider that IWG has been in talks with multiple potential partners but failed to agree terms with any of them; either it’s reflective of management’s confidence in the future growth or they’re holding out for too high a price," said Neil Wilson, chief market analyst at Markets.com.
IWG posts sharp fall in first-half profits
Alongside its announcement that talks with the three remaining suitors had collapsed, IWG reported a 33% drop in pre-tax profit to £54.3mln for the first half. It blamed investments in refurbishments and talent, higher marketing spending and a weak UK market.
Group revenue rose 2.9% to £1.2bn, buoyed by an improvement in the Americas and Europe, Middle East and Africa and “good growth” in Asia.
The company said it was confident of achieving full-year results in line with expectations. It raised its interim dividend by 11% to 1.95p.