EL PASO, Texas —  A 15-year-old missing since early July is considered endangered after authorities learned she may be with a registered sex offender, El Paso police said Wednesday.

Stephanie Herrera vanished on July 2 and was initially treated as a runaway. But this week investigators learned she may be on the run with Roger Dale Johnson, a sex offender wanted for failing to register with El Paso police, Officer Chris Mears said.

The girl is believed to have left on her own, Mears said.

Johnson was convicted in 2005 of indecency with a child by sexual contact. According to the state's sex offender database, Johnson's crime involved a 7-year-old girl.

Stephanie's family has told police that the girl was previously ordered by her mother not to see Johnson, though the exact nature of their relationship was unclear Wednesday.

Mears said Johnson may have connections to the Amarillo area.