TWITTER Inc shares plunged on Thursday as fears mounted that a much-anticipated auction of the social media company will draw minimal interest from potential buyers.

With stagnant user growth and continuing losses, Twitter's board agreed last month to consider a sale, and has told potential acquirers it wants such deliberations to conclude by the time it reports third-quarter earnings on Oct. 27, Reuters reported on Wednesday.

Technology website Recode reported later on Wednesday that Alphabet Inc's Google, long considered the most logical buyer for Twitter, and Walt Disney Co would not bid for the social network, leaving cloud software company Salesforce.com as the only known suitor.

Twitter shares fell as much as 19.2 percent to US$20.10, valuing the company at about US$14.2 billion. They closed 20.1 percent lower at US$19.87.

Salesforce Chief Executive Mark Benioff has publicly expressed his interest in Twitter in recent days, but stopped short of saying the company had decided on a bid.

Analysts said he downplayed the possibility in a meeting with investors on Wednesday, sending Salesforce shares up about 4 percent.

"I'm not saying I'm buying it, but I'm not saying I'm not buying it," Benioff said on Wednesday in an interview with the New York Times.

Even at US$20, Twitter shares are well above the US$14 they were trading at before speculation about a possible acquisition began to emerge this spring.

Many investors and analysts believe Twitter remains expensive for most potential buyers, but the company does not have a clear back-up plan if it is not acquired.

Product initiatives under CEO Jack Dorsey, who returned to the company a year ago but also remains CEO of payment company Square, have borne little fruit. Large amounts of employee stock and options are also considered an obstacle for some potential bidders.

The rationale for Salesforce bidding on Twitter is not clear, said Jefferies analyst John DiFucci in a note to clients. Buying Twitter would reduce the value of Salesforce shares by about US$11 through dilution, while increased debt could cut another US$9.50 from the stock.

Other potential bidders beyond Salesforce are taking a look at Twitter, CNBC said, citing sources.

Apple Inc has also been rumored as a possible bidder, though Recode reported that Apple would not move forward.