Gone are the days when a toy company could simply blitz Saturday morning cartoons with ads.

WowWee focused much of its effort on YouTube, where children go to watch other children play with toys in a phenomenon called “unboxing”

The toy company sent Fingerlings to key “influencers” on YouTube — two preschool “besties” who make videos about their trips to a playground and a skinny girl with faded fingernail polish who publishes daily posts about toys. Some influencers were paid to promote the monkeys; others did it for fun.

Mackenzie Ziegler, a dancer with more 1.7 million YouTube subscribers, and her friend Lauren wrapped multiple monkeys around their fingers and mugged for the camera.

“They are so cute,” Ms. Ziegler told her followers.

Image A video of Maya Vallee-Wagner’s reaction to Fingerlings, taken by her father, went viral after WowWee posted it on Facebook.

In another video, a Fingerling takes a ride on the E train, and appears to visit a bar.

Not long after the social media push in August, the monkeys were basically sold out everywhere, and WowWee was able to pull back on its marketing.

“It’s a wonderful problem when your demand outstrips supply,” said Mr. Gottlieb, the toy analyst.

But managing supply can be a delicate balancing act. If WowWee fails to deliver enough Fingerlings by Christmas, it could miss the moment when the fad reaches its peak, or alienate desperate parents who feel manipulated by the hype.

“It’s really not fair,” one woman posted on Facebook. “People work and no one has time to stalk” toy stores.