Today: Shares in Oakland-based Pandora hit an all-time high after strong gains in listenership and a new ad deal. Meanwhile, Twitter's roller-coast ride took a dip, as it received another stock downgrade.

Pandora shares sail, while Twitter sinks

Twitter and Pandora shares were on opposite ends of the spectrum Monday, as Twitter sank while Pandora soared to a record high.

Shares in Pandora, the Oakland-based Internet radio pioneer, jumped more than 14 percent, or $3.90, to close at $31.49, on word of a growing audience and a new advertising deal. Pandora reached a new intraday high at $32.45, and ended the day with its second-best closing price ever. Shares are up more than 200 percent in the past year.

Pandora reported Monday hefty year-over-year gains for the month of December, including a 13 percent gain in listener hours, from 1.39 billion to 1.58 billion; a more than 1 percent rise in total U.S. radio market share, from 7.58 percent to 8.6 percent; and a 13 percent jump in active listeners, from 67.1 million to 76.2 million.

The numbers are a double-edged sword for Pandora; more listeners also means it has to pay more money in royalties to music labels. Pandora has yet to make a profit, but its steady growth has analysts believing it will before too long.

Investors were even more pleased by another Pandora announcement Monday, that it was launching advertising for its in-car app. Pandora has about 4 million in-car listeners, up 244 percent over last year, and has its sights set squarely on Sirius XM, the industry leader in car-based streaming music.

"Nearly half of all radio listening takes place in the car. . . . We are now seizing the opportunity to connect advertisers with a more targeted audience than traditional radio can provide," Pandora Chief Marketing Officer Simon Fleming-Wood said in a statement.

The 15- to 30-second ads will run across 130 vehicle models, and Pandora notes its app is available in nine of the top 10 best-selling cars in the U.S. The company said the in-car app will run fewer ads than any other of its platforms, and Pandora One premium subscribers will still get ad-free listening. Major advertisers such as BP, Ford, State Farm and Taco Bell are already on board.

Meanwhile, stock in Twitter, the San Francisco microblogging company, dropped 3.9 percent, or $2.71, to $66.29, after dipping as low as $63.50 on Monday following another downgrade. Morgan Stanley analyst Scott DeWitt cut his rating from "equal rate" to "underweight," or sell, as he believes Facebook is in a better position to generate online advertising revenue in the coming years.

DeWitt said that while Twitter is "compelling," it's at risk of becoming a "niche product" and may find it difficult to expand, according to a report by MarketWatch. "Despite the ease at which users can sign up for Twitter, we think it is inherently more complicated to understand how to get the most out of Twitter compared to Facebook's service, which is easier to use," DeWitt said in a note.

DeWitt also raised his price target for Facebook to $62 a share, up from $53. Facebook shares shot up 4.8 percent, or $2.64, to $57.20.

Twitter has seen gains over the past month that has left many analysts shaking their heads and feeling the company is overvalued. Shares rose nearly 70 percent in December, before plunging 19 percent in a two-day drop toward the end of the year. That had many experts believing reality was setting in, but then, as fast as it dropped, shares rebounded, recovering nearly all of its losses last week after Evercore analyst Ken Sena praised its strong position in video advertising.

Up: Apple (AAPL), Google (GOOG), Cisco (CSCO), Facebook, Zynga, Pandora

Down: Oracle (ORCL), Intel (INTC), HP, eBay (EBAY), Yahoo (YHOO), Netflix (NFLX), LinkedIn, Tesla, Twitter

The SV150 index of Silicon Valley's largest tech companies: Up 2.57, or 0.17 percent, to 1,482.60

The tech-heavy Nasdaq composite index: Down 18.22, or 0.44 percent, to 4,113.68

The blue chip Dow Jones industrial average: Down 44.89, or 0.27 percent, to 16,425.10

And the widely watched Standard & Poor's 500 index: Down 4.6, or 0.25 percent, to 1,826.77

Check in weekday afternoons for the 60-Second Business Break, a summary of news from Mercury News staff writers, The Associated Press, Bloomberg News and other wire services. Follow Mike Murphy at Twitter.com/mmmmurf.