Known in the press as "Little So Ji-sub" for his resemblance to the said actor, in 2013 Yoo starred in the music video for So's single "Eraser" together with Park Shin-hye. This was his second time promoting So's musical endeavors, after "Lonely Life" in 2008. Following that, Yoo's first photo book titled Travel Letter, Spring Snow, And... was published; it was the last project shot by celebrity photographer Bori before her death on April 9, 2013.
Yoo enlisted for his mandatory military service in the army on March 5, 2013, where he reportedly became an instructor training new recruits. He was discharged on December 4, 2014.