It was only days old, but already "Pokemon Go" had an iron grip on America: mobs of people wandering neighborhoods, parks and urban thoroughfares searching for imaginary creatures on their smartphones.
Lured by the nostalgia of the popular 1990s franchise and intrigued by the game's new augmented reality, "Go" users walked blindly across busy streets, strayed into a police station and came together with flash-mob-like quickness in municipal parks across America.
The phenomenon pushed past the usual lines of containment so quickly that police in the town of Duvall, northeast of Seattle, even issued an advisory – albeit tongue in cheek:
"We have had some people playing the game behind the PD, in the dark, popping out of bushes, etc. This is high on our list of things that are not cool right now," police cautioned. Instead, they advised, gamers should "come on in to the lobby … and let someone behind the counter or an officer know you are looking for an imaginary critter thing."
The craze sent Nintendo's stock soaring, adding $7.5 billion to the video game maker's market value. By Monday, "Pokemon Go" already had more downloads than the popular dating site Tinder and was already poised to surpass Twitter in daily active users on Android devices. It ranked above Facebook, Snapchat and Instagram in the Google Play store.
Users have been hunting down Pokemon in offices, schools, hospitals and backyards. Many come together in parks and at well-known landmarks in their quest to electronically gather Pokeballs.
The balls are then hurled at the game's pocket monsters to capture them. Players often visit sites such as churches, which digitally become "gyms," where battles are fought.
On Monday, Jonathan Makepeace and his buddies Nick Anderson and Ethan Ingersoll were tracking a Pokemon creature in Central Park in New York.
Ambling around a corner, they stopped short, facing a clump of bushes next to the walking path. Then the three 18-year-olds swung their smartphones to attention.
"Execute!" Anderson yelled as they swiped across their screens.
With 150 Pokemon to collect — plus the chance to rumble with opposing players — "Go" stands to energize the "Pokemon" franchise, which includes playing cards and cartoon shows.
Makepeace and his friends have been playing the original Pokemon from the beginning — the Game Boy version debuted the year they were born. Now, with a free summer after graduating high school, they ditched their go-to Nintendo "Super Smash Bros." sessions for some fresh air. They spent four hours one recent evening prowling the Upper East Side searching for Pokemon, they said.
"As you walk down Park Avenue, you'll see Pokemon on an Art Deco relief or on a statue on a building that you've never noticed before," Anderson said.
One well-known relic even plays a role in the game. Cleopatra's Needle, the Egyptian obelisk tucked in a quiet corner of the park, acts as a meeting place for players to face off against their opponents.
In Exposition Park in Los Angeles on Monday, "Go" players staggered back and forth across the lawn of the Natural History Museum of Los Angeles County, heads down, eyes glued to their phones.
Jose Gonzalez, 15, paused to rest in the shade under a tree. "I just caught one right now, a grass type," he said.
At the main entrance to the Exposition Park Rose Garden, more than 20 people who had just met up chatted and exchanged Pokemon advice. Victor Gracia, 28, said she had set up "mods," or lures, to draw fellow Pokemon users to the location.
One of those lured to the park was Matteo Tanaka, 19. He said he's spent at least 50 hours on the game since it debuted last week. "You walk by and say, 'Hey, are you playing Pokemon Go?'"
But already the game has posed risks and warnings that users may be drawn into danger.
Armed robbers in Missouri used the app to lure victims to isolated locations, police said. Others have been injured chasing the imaginary characterswithout paying attention to their real-life surroundings.
Police in Darwin, Australia, said they have discovered people trying to find Pokemon characters at their building, and they warned players to be safe.
"It's also a good idea to look up, away from your phone and both ways before crossing the street," police suggested.
Washington state's Department of Transportation warned against "Pokemoning" while driving.
The game has led to some grisly discoveries as well. A quest to find Pokemon led a teen to discover a dead body in a river in Wyoming.
"I was walking towards the bridge along the shore when I saw something in the water," Shayla Wiggins, 19, told KTVQ. "I had to take a second look and I realized it was a body."
The frenzy accompanying the game's rollout amazed investors and boosted the fortunes of Pokemon Co., game developer Niantic Inc. and investor Nintendo. Nintendo has struggled in recent years to produce a hit that comes close to matching the success of its 2006 console, the Nintendo Wii.
The Japanese video game giant, with North American headquarters in Redmond, Wash., recently refocused its mission, selling off its majority ownership of the Seattle Mariners.
"We thought the game would be popular," said Niantic Chief Executive John Hanke, "but it obviously struck a nerve."
Times staff writer Evans reported from Los Angeles and special correspondent Anderson from Seattle.
Staff writer Tracey Lien in San Francisco and special correspondent Matt Hansen in New York contributed to this report.
8:06 p.m.: Updated throughout.
1:27 p.m.: This article was updated with information on Nintendo's stock price as well as quotes from analysts and "Pokemon Go" players.