Bob Pearson, head of communities and conversation at computer company Dell, said his company had generated $1million (£610,000) in sales through alerts posted to Twitter.

PR staff at PepsiCo posted messages on the site after users began criticising of one of the company’s advertisements, which depicted a cartoon calorie committing suicide.

Huw Gilbert, communications manager for PepsiCo International, “tweeted”, or posted a public message, in reply.

“Huw from Pepsi here,” he wrote. “We agree this creative is totally inappropriate; we apologise and please know it won’t run again.”

One member “tweeted” back: “Thank you . . . for having the guts to get on Twitter on behalf of Pepsi and give us an update on the suicide ad.”

Other companies that have accounts to promote products and provide customer service on the website include Comcast, JetBlue and Home Depot.

Scott Monty, head of social media for Ford Motors, used Twitter to answer criticism about the way his company had filed a lawsuit against a website selling unauthorised bumper stickers.

Fans of the site posted angry messages but Mr Monty used Twitter to explain the company’s position.

He told the Financial Times: “Part of my job is to humanise the company – you want to interact.”

Earlier this month, Mike Wilson, 37, a software engineer from Denver, Colorado, escaped alive from a plane crash at Denver international airport and made headlines when the first thing he did was post an immediate account of the incident on Twitter.