Police say they received an anonymous tip that 13-year-old Savanna Marie MacMullet of Radnor and 20-year-old Ashley Ryan Hareford of Virginia were spotted in the area of 30th Street Station around 4:30 p.m.
Authorities say they boarded a Megabus to Washington D.C.
U.S. Marshals were waiting for the two as they arrived at a D.C. bus stop at around 7:00 p.m.
"Police were there. They had no idea so it was a peaceful resolution to this situation, which we're happy [about] cause we have to remember, she's 13 years old, we didn't want any extra trauma to be added to this," Lt. Christopher Flanagan of the Radnor Police Department said.
Hareford was taken into custody without incident at the scene. He is facing a corruption of minor charge and could possibly face more charges.
The girl's family was relieved to hear police located their loved one.
"I was so glad, I couldn't believe it. It was just so scary knowing she was missing and it's just amazing that they found her," Savanna's great aunt Mary DeWees said.
The girl has since been reunited with her family and as of Wednesday morning she was being checked out at Bryn Mawr Hospital.
Police were not classifying MacMullet's disappearance as an abduction. They believed she took off willingly with the 20-year-old.
Police say the pair met online.
A Radnor Township officer came across Hareford outside of the victim's home on Sunday night. Nothing appeared to be wrong, but police stopped the man because he seemed suspicious. He was ultimately released.