The victim was near the valet parking area when a black male about 5 feet, 10 inches tall with short black hair approached him, Hansen said.
The assailant stuck a small handgun in the victim's side and took a wallet containing $2,700, Hansen said.
The suspect was seen running toward the Turf Motel on East Washington Street and police fanned out in the area in an attempt to locate the robber, Hansen said.
Police waited to determine if the robber would show up in the parking lot of the motel but he never did, Hansen said.
A police dog unit from the Martinsburg Police Department was used in an attempt to locate the robber, Hansen said.
The dog picked up a scent where the robbery occurred and led investigators to the rear of the Charles Town Athletic Club at 620 E. Washington St., Hansen said.
The dog stopped at a fence behind the athletic club but police never saw the robber, Hansen said.
Police said the robber was clean-shaven and wearing black pants and a blue shirt. Anyone with information about the robbery may call the sheriff's department at 304-728-3205.
A track spokesman said the track has surveillance cameras in the parking lot where Tuesday's robbery occurred. Track officials are reviewing the tapes.
Vice President of Public Affairs for Penn National Gaming Eric Schippers would not say whether the track has increased security because of the robberies. Schippers said track officials always are reviewing their security procedures to make sure patrons are safe.
"Security is very tight," Schippers said.
The track has a staff of more than 100 security officers who are constantly on the lookout for anyone acting suspiciously at the track and the track has surveillance cameras in the parking garage, Schippers said.
Patrons who win large amounts of money at the track are encouraged to receive their money by check rather than cash, Schippers said.
The earlier robberies involved victims who were on their way home from the track. One occurred May 2 and the other occurred May 21.
The May 2 robbery occurred about 5 a.m. in Ashburn, Va., when the victim said his car was rear-ended by a Cadillac on Va. 7. Both drivers got out and the victim told investigators the Cadillac driver suddenly attacked him and stole nearly $2,000.
The May 21 robbery occurred about 9:45 p.m. when a woman had car trouble on Va. 287 in Purcellville, Va. A man in a yellow pickup truck stopped, but rather than help, the sheriff's office said he pulled a gun and made off with more than $3,000.
Both victims were slightly injured.
Loudoun County Sheriff's Department spokesman Kraig Troxell said his department is still investigating the robberies. Troxell said investigators are trying to determine if the May 2 robbery may be tied to the track, including the possibility that someone may have followed the victim from the track.
Troxell said he thinks the May 21 robbery may have been a "crime of opportunity," although investigators may reassess the situation depending on what they learn about Tuesday's robbery.