Napster Inc. on Tuesday raised its fourth-quarter revenue guidance due to a jump in subscriber growth and stronger-than-expected sales of music downloads, sending its shares soaring as much as 18 percent.

The L.A.-based online music distributor said it now expects revenue of between $16.5 million and $17.5 million for the fourth quarter, up from a prior estimate of about $15 million.

The company said its subscriber base grew by 143,000 in the fourth quarter to total more than 410,000, including 56,000 university subscribers. This represents sequential quarterly subscriber growth of more than 53 percent.

The company said its “Napster to Go” marketing campaign helped spur the growth in subscribers, and that pay-per-download music purchases helped push sales higher.

On March 3, Napster boosted its fourth-quarter revenue estimate from $14.1 million to $15 million.