Hey there, Facebook and Twitter do not have a limit for hashtags but there's a thing: Tweets are restricted to 140 characters so you don’t want a hashtag taking up 50% of the letters in your tweet. On Facebook you don't have a limit of characters but yopu don't want to annoy your fans or friends with too many hashtags. Use a maximum of two hashtags in your tweets or Facebook posts. Otherwise, Instagram has a limit of 30 hashtags per photo.
I think you can use hashtags to discuss a certain point, like #valentinesday, #birthdays and #others. Make sure you do not over use them.