It is almost exclusively used in informal settings among friends.
In the phrase "Ell sien TEREZA ESTOU A BAZAR," it appears you are using the artist name (a musical artist known for tracks like "Novidades Da Banda") combined with a message to someone named Tereza stating that you are heading out. Ell sien TEREZA ESTOU A BAZAR
In Portugal, this means to joke or make fun of someone, though visitors should be careful as it has a much more explicit sexual meaning in Brazil. It is almost exclusively used in informal settings