The 26.2-mile route stretched from Dodger Stadium to the Santa Monica Pier.
E! News said Baldwin, an Ironman triathlete and officer in the U.S. Navy, was the top celebrity runner, completing the trek in 3 hours and 24 minutes.
Chef and television personality Ramsay dropped out nearly two-thirds of the way through the marathon, the New York Post said.
"Damn, had to stop at 15 miles, just felt my calf muscle go," the Post quoted Ramsay as saying via Twitter.
Actor LaBeouf finished in 4:35 and former child star Astin in 5:16. E! News said reality TV personality Patridge finished the marathon, but her time was not known.
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