Valentine's Day in 2017 is the first Valentine's Day event in Pokémon GO.
Trainers received double candy for catching, hatching and transfer of Pokémon. The required Buddy distance was a half of its regular amount, which meant 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. 
Moreover, during the event there was higher chance to hatch following Pokémon: