Luckily, there may be more opportunities to catch a shiny Pikachu than any other Pokemon. Shiny Pikachu doesn't look that different when compared to the normal Pikachu. The color scheme is essentially just a brighter, more golden version of the Pokemon mascot.
Like any other shiny Pokemon in Pokemon GO, there is no sure-fire way of obtaining a shiny Pikachu. The best way for a player to increase their chances of finding a shiny Pokemon is by using incense. This will make wild Pokemon appear around the player for a short amount of time.
While incense can make Pokemon appear around players, it can't guarantee a Pikachu. For that, Pikachu needs to be part of the roster of Pokemon that appears in the wild at the time. This can change depending on the nests of Pokemon that rotate or a change in events that dictate options around the area.
Pikachu and the different Pokemon GO events it can be found in
One major event that can change the number of Pikachu in the area is spotlight hour. Spotlight hours are generally scheduled each week on Tuesday nights. However, each week focuses on a different Pokemon, so it's highly unlikely to see the same Pokemon in the spotlight anytime soon.
During the spotlight, the selected Pokemon will appear all over the place for an hour. Some bonuses will also pop up depending on the week, such as extra experience per catch or additional stardust.
For many events in Pokemon GO, Pikachu will get an event theme and a shiny version. This means that players should be on the lookout for the next Pikachu event outfit.
Waiting for a new event is, therefore, the best bet for players to get their hands on a new shiny Pikachu.