For investors in Yelp (YELP - Get Report) , patience may finally be paying off. 

The Internet company rewarded investors with a strong first quarter fueled by impressive growth in local advertising revenue that caused its stock to soar. And analysts think the stock could have even more upside.

On Thursday after the markets closed, the consumer review site posted $158.6 million in revenue and earnings per share of 8 cents, compared to analysts' estimates of revenue of $155.6 million and EPS of 3 cents.

Shares of Yelp are up more than 18% Friday morning to $25.36 a piece.

The San Francisco-based Internet company attributed strong financial results to a 40% increase in local ad sales, in addition to growth in transaction revenue. Yelp also raised its guidance for the full year to a range of $690 million to $702 million, from $685 million to $700 million previous. For the second quarter, it is expecting revenue to be between $167 million and $171 million.

"Haven't seen this from YELP in a long time," RBC Capital Markets analyst Mark Mahaney wrote in his note Thursday night, noting that shares of Yelp could go even higher.

Yelp's growth in local advertising is a "huge win," said Jim Cramer, TheStreet's founder and manager of the Action Alerts PLUS portfolio, who previously had been pessimistic about the company. He explained that local merchants are liking the Yelp platform more and more, and as a result, are willing to pay to have their restaurants featured at the top of search results.

For Yelp, which has been one of the biggest under performers in the Internet sector with it stock down more than 50% in the last 12 months prior to Friday's pop, local ad revenue growth may be at a "positive inflection point," Mahaney noted, adding that the current valuation has limited downside and material upside within 12 months.

"We still see in Yelp a strong and improving local solution and an asset with significant strategic value, facing a way under-penetrated market opportunity," Mahaney wrote. "We believe we stand here on the precipice of a fundamentals inflection for an expensive stock with negative sentiment."

Yelp seems to be back on track, said B. Riley analyst Sameet Sinha via phone, while cautioning that results from one particular quarter don't necessarily mean that Yelp has successfully turned itself around.

The review site, which went public in 2012, has been struggling with sales productivity, traffic and general operations, Sinha explained. (Sales productivity is measured by the local ad revenue that each salesperson brings in.)

"They figured out what the problem was, and they're fixing it," he said. "It takes time. It hasn't been easy for the [past] four quarters."

The strong first quarter also comes after Yelp was the target of buyout discussions last year. Nothing came to fruition from the talks, however.

David Einhorn's Greenlight Capital revealed to its investors earlier this week that it has purchased shares of Yelp, noting that the company was well-positioned to double revenue by 2019.

Sales productivity is estimated to increase about 6% year over year in the first quarter, Cowen & Co. analyst Kevin Kopelman wrote in his note Friday morning, adding that this growth sets the company up for potential revenue upside for the rest of the year.

Local advertising revenue was helped in the quarter by sales productivity and ad optimization, including ad targeting and new products, Kopelman added. He also noted that margin pressure from sales and marketing expense is also better, increasing his price target to $25 from $21.

And there's more change coming to Yelp. New CFO Lanny Baker, who was most recently the CEO of ZipRealty and previously served as the CFO of Monster Worldwide (MWW) , starts at the company on May 9.