After receiving tips, federal marshals in D.C. located 13-year-old Savanna Marie MacMullet and 20-year-old Ashley Ryan Hareford at a bus station.
Hareford was taken into custody without incident at the scene.
He is facing corruption of minor charges.
Police were not classifying MacMullet's disappearance as an abduction.
They believed she took off willingly with a 20-year-old man.
Savanna was last seen in the Garrett Hill section of Radnor Township at 4:00 p.m.
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.
Thomas MacMullett was very concerned for his daughter's safety.
"It seems like it's just him and her on that Facebook page," said Savanna's father, Thomas MacMullett. "It's almost like a memorial dedicated specifically to the two of them. It's kind of creepy."
"We're concerned for her safety," said Radnor Police Lieutenant Christopher Flanagan earlier in the day. "When a child is missing - she's 13, he's 20. She hasn't checked in with her family. We are concerned."