Maguire Properties Inc. shares jumped 24 percent Thursday after founder Robert F. Maguire III said he increased his ownership in the real estate investment trust and its operating partnership to more than 19 percent, and intends to become more active in the company from which he was ousted last May.

Maguire, who was forced out of his chief executive job after he failed to take the real estate investment trust private, reported in a Securities and Exchange Commission filing that he bought about 1.6 million common shares of the REIT between Dec. 9 to Jan. 13 for about $3 million.

Maguire Properties, considered downtown L.A.’s largest office building owner, has seen its share price plummet 92 percent over the past year as the once booming Southern California office market faltered in the economic downturn.

Maguire now owns 4.7 million shares, or 9.8 percent, of common stock, making him the largest individual shareholder and fifth largest overall. Maguire said in a press release that he is considering acquiring more, or even all, outstanding shares of the company’s common stock. He also plans to hold discussions relating to the strategic direction of the company with company officers, potential strategic partners, investment and finance professionals.

Nelson C. Rising took over as president and chief executive after Maguire was ousted by the board. Maguire has since increased his focus on his general aviation company, Maguire Aviation.

Maguire declined through a spokesman to comment beyond the press release. A Maguire Properties spokeswoman said the company isn’t commenting on Maguire’s filing.

Maguire Properties shares closed up 43 cents to $2.25 on the New York Stock Exchange after the late morning announcement.