Forever 21 Inc. has sold its headquarters building to Blackstone Group, industry sources confirmed. The Lincoln Heights property sold for just under $166 million, according to data from CoStar Group Inc. Forever 21 did not return requests for comment. It is unclear if the fast-fashion retailer will remain in the building. Blackstone declined to comment. The building, at 3880 N. Mission Rd., is a 2.1-million-square-foot industrial facility that Forever 21 purchased from Macy’s Inc. for $38 million in 2010. Forever 21 is a private company founded by Do Won “Don” Chang and Jin Sook Chang. The company had roughly $4 billion in revenue in 2017, according to Business Journal estimates. It was the sixth largest private company in L.A. County.