TheBurg announced the deal on its website.
"Alex is making a major investment so that TheBurg will be an even better paper for the Harrisburg community," the paper wrote on its Facebook page.
Co-founder Lawrance Binda will lead TheBurg's operations on a day-to-day basis as editor-in-chief. Hartzler is now the publisher.
Peter Durantine, the paper's co-founder and former editor, and Angela Durantine, co-founder and former advertising executive, have sold their interest in the paper to pursue new opportunities.
Terms of the sale, including all assets of Three Bridges Media, were not disclosed.
"Our vision of a vibrant, revitalized urban core is one and the same," Hartzler said in a statement in TheBurg's announcement. "I commend Pete, Angela and Larry for starting a newspaper that has come to mean so much to the people of the Harrisburg area."
Hartzler plans to make significant investments in the paper, including staff expansions, publishing more in-depth stories and improving both the print edition and online presence.
TheBurg, which began publishing in January 2009, will resume publication in March after a two-month break, according to the post. The paper also has relocated to 403 N. Second St.