Colorado Army National Guard joins search for missing hiker in Rocky Mountain National Park

The Colorado Army National Guard has joined the search for a 23-year-old hiker who has vanished inside Rocky Mountain National Park while scaling its tallest peak. 

Lucas Macaj of Colorado Springs remains missing Thursday after he was last heard from early Sunday afternoon "when he texted a friend indicating that he was on the summit" of the 14,259 ft. Longs Peak, the National Park Service says. 

"It’s hard to think about, especially with all the thoughts that come with it," his girlfriend, Natalie Dodgen, told 9NEWS.