As Granblue Fantasy has built-in integration with your Twitter account, it is very common to use TweetDeck to find raids to join. However, players using the English version are much less common than players using the Japanese version, so it can be easier to find raids using the Japanese search terms. Here is a list of the common raid bosses; simply copy the Tweet term into your TweetDeck search bar.
PLEASE NOTE: If you are aiming for high-attendance raids such as Grand Order or Proto Bahamut, some players spoof other raids by copying the search term into their in-game Tweet, which will cause raids you do not want to appear in your TweetDeck search columns. You can check the picture in the Tweet before you join the raid, but people can also copy entire old Tweets, picture and all, and simply replace the raid ID with a new raid, so also check the picture in game when selecting your support summon. In the case where you still accidentally join the wrong raid, if you do not attack, summon, or use any skills, your EP will be refunded after the raid boss dies, so keep that in mind.