Just as Jimmy Fallon’s new run on “Tonight’ takes off, a group of advertisers is tackling the likable late-night host and trying to make him take part in their promotions.

Since Fallon launched his “Tonight” tenure on February 17, advertisers appear to be hanging on his every word. After he discussed his desire to purchase a truck on the March 5 edition of the show, Ford, Nissan, General Motors and Dodge’s Ram Trucks all issued tweets attempting to make a sale.  Ram even parked one of its vehicles outside the “Tonight” studio at NBC’s venerable 30 Rockefeller Center headquarters with a sign asking the comic if the truck met with his approval.

Last week, Ocean Spray, the cooperative of cranberry and grapefruit growers, asked followers of its Twitter feed to tell Fallon of the availability of “cranberry sauce singles,” a sandwich condiment the host has called for on “Tonight” and from his previous perch at NBC’s “Late Night.” The tweets are part of an effort the company has been making for the last nine or ten months, estimated Thano Chaltas, Ocean Spray’s global chief marketing officer.

“We don’t have a ‘buy’ in ‘The Tonight Show,’ Chaltas said. “Who knows what things could grow in the future?”

Thanks to social-media, advertisers no longer need to wait until 11:30 at night to get their promotions alongside late-night’s most popular personalities. Nor do they have to buy TV time to align themselves with the most popular boob-tube fare. Instead, they can post promotional items on Twitter, Facebook and elsewhere that tie their pitches to well-watched programs or other topics trending in the digisphere – and then hope consumers find the connections relevant and interesting.

“You don’t just put out an organic note and think that people are going to find it,” said Anne-Marie Kline, a senior vice president at digital-marketing specialist Digitas. Getting into a consumer’s social-media “feed” is becoming more important for marketers, she said, “and understanding how to get in the feed and how to make sure a brand shows up there is what we are trying to do.”

The interest in social-media advertising linked to Fallon comes as ad revenue for NBC’s “Tonight Show” has dwindled. In 2012, for instance, “Tonight” under Jay Leno captured approximately $159.8 million, according to Kantar, a tracker of ad spending. In 2013, before Fallon took the reins of the show, ad revenue totaled around $135.4 million, representing a drop of nearly 15.3% from 2011. NBC was not able to make ad-sales executives available for comment and a “Tonight” spokeswoman said producers declined to comment on advertisers’ social-media activity related to the program.

Ocean Spray has followed Fallon for some time, both during his tenure on “Late Night’ and his current run on “Tonight,” said Chaltas. When Fallon paid a visit to Boston’s Faneuil Hall, Ocean Spray, based in Lakeville-Middleboro, MA, was there to greet him with a pair of waders used by workers in cranberry bogs. As Fallon has urged viewers to consider the idea of “sauce singles,” Ocean Spray made a funny video and urged its followers to retweet it and get Fallon to respond.

“We wanted to, obviously, get his attention. We wanted to respond to his challenge,” said Chaltas. And Ocean Spray also wanted to grab consumers’ attention “in a new and fun way” that wouldn’t involve all the deliberation and expense necessary to mount a TV-ad campaign.

The Twitter flurry is the result of a new emphasis some advertisers are placing on what is known as “real-time marketing,” or seizing upon popular items in the ebb and flow of social media to try to make an impression on consumers. Such stuff first came to notice during CBS’ 2013 broadcast of Super Bowl XLVII. When the network suffered from a power outage just after the second half got underway, Oreo – already a sponsor of the game – sent out a clever tweet about dunking the cookie in the dark. The item was retweeted more than 10,000 times according to 360i, a digital marketing agency that created the tweet for the cookie maker.

Since that time, such stuff has become more commonplace. Before this year’s Super Bowl broadcast, Progressive Insurance had its longtime spokescharacter, Flo, tweet the following:

When musician Pharrell Williams was spotted wearing an intriguing cowboy hat during CBS’ broadcast of this year’s Grammy Awards, roast-beef chain Arby’s asked if the hat looked a little too much like the one it uses in its logo.

Bonus: Williams responded!

The cost of social-media campaigns makes testing such ideas easy. “The investment for any specific action you take is relatively low, and so you can take a lot of swings at bat,” said Shankar Gupta, vice president of strategy at 360i. Ocean Spray’s Chaltas estimated his company’s recent Fallon-related efforts cost “a couple of thousand dollars” for the tweets and making certain the video was distributed properly on Twitter. The cost of running a 30-second spot on any of the broadcast-network late-night programs has in recent years hovered around $50,000, according to ad buyers.

As such, even the smallest marketers are taking part in the rush to tweet. When Scripps Networks International recently announced actor William Shatner would take part in a reality series about renovating his home, a small home-insulation company in Mahwah, NJ, known as Frost King, tried to hitch itself to the news:

As more advertisers join the fray, however, some concern is emerging their efforts will annoy the people they want to attract. If marketers “just kind of swing at everything, we are going to ultimately reach a point where people get really tired of it,” said 360i’s Shankar. “People got tired of email marketing, because of spam. And pop-ups,” he added. “It behooves us all to make sure we are identifying the right opportunities for our brands – to ensure we don’t sort of try consumers’ patience.”