Valentine's Day is a seasonal event in Pokémon GO that takes place in February to celebrate real-world Valentine's Day.
2017 Valentine's Day event took place from February 8th through February 15th, 2017.
Trainers received double candy for catching, hatching and transfer of Pokémon. The required Buddy distance was a half of its regular amount, which means that Pokémon received candy twice as fast.
Additionally, Lure Modules lasted up to six hours, rather than their normal 30 minutes.  After the event concluded, lures continued to last 6 hours until Saturday, February 18th, 4 p.m. (PST). 
The following Pokémon had been confirmed to have increased spawn rates, according a various players around the world. 
Pokémon Eggs hatchlingsEdit
During 2017 Valentine's Day event there was higher chance to hatch following Pokémon:
2018 Valentine's Day event lasted only for three days as it took place between February 13th and February 15th, 2017.
Trainers were awarded with 3 times more Stardust for each capture of Luvdisc and Chansey. 
Luvdisc and Chansey had increased chance of spawn in the wild for the time of this event and there was also Shiny Luvdisc released with the start of the event.