The research, carried out by LexisNexis, showed that people are now more likely to share negative feelings towards a brand online than they were a year ago.
Just over half polled said that if they are unhappy with something they have bought or used they will complain about it online. Two-thirds said that when they'd shared bad feedback about a company online, they'd not had a response from the company in question.
Bob De Laney, director of new business at LexisNexis UK, said: "This represents a massive missed opportunity for companies and brands to engage with unhappy customers. Sixty-seven per cent of complainants have been ignored, leaving them to act as influential detractors online, potentially having a negative impact on other purchasers' behaviour."
He said that although companies could not monitor all comments made in private Facebook pages, for example, they were missing an opportunity to turn detractors into promoters by failing to keep up with what was being said.
In better news for brands that are getting it right, good experiences about brands are likely to spread slightly faster than bad ones. The research found that 62% of respondents would share their views online if they were "delighted" by a product, again with people saying they were more likely to do so than in the past.
The survey questioned 1,002 people. Further findings will be made available at LexisNexis' presentation at the Online Information 2009 conference.