MANSFIELD (CBSDFW.COM) – Parents and residents are on alert after a man driving a blue pickup truck twice asked a 12-year-old girl if she needed a ride and trailed her down the street when she declined on Monday.

In a release issued Tuesday evening, Mansfield Police Department spokesman Thad Penkala said the incident was being “aggressively investigated” by Mansfield PD, Mansfield ISD and the Texas Rangers.

The suspicious man approached the girl at about 6:40 p.m. Monday while she walked home from tennis practice. She told the man “no” twice, and when he continued to follow her she turned and ran in the opposite direction.

Someone driving by thought the scene was odd and pulled over to make sure the girl was OK.

That Good Samaritan gave the girl a ride home and then called Mansfield Police, offering the girl’s address to investigators.

“This child knew what she needed to do and a Good Samaritan stopped,” said Elizabeth Hostin, a principal at Linda Jobe Middle School in the Mansfield Independent School District.

Mansfield ISD officials sent students home with a note Tuesday to give to their parents and then followed up with an automated message.

“You received a letter from the principal about an incident that occurred yesterday after school,” the phone message said. “A girl walking home was asked by a Hispanic male in a dark blue pickup if she wanted a ride.”

Penkala said police have interviewed the girl and are now looking to find the man and his truck. The pickup truck is dark blue with a camper shell, “bad paint” and drives low to the ground.

The suspect is believed to be a Hispanic man in his 30s with brown hair, “blood shot eyes,” clean-shaven and who speaks in “broken English,” Penkala said.

Parents in Mansfield ISD said they were stunned at the news.

“It’s very disturbing, my kids go here and I’m glad I’m picking them up,” said Toney Phillips, a parent.

The concern is even greater now. Last week in Mesquite, police say a man lured two young girls in his car and exposed himself to them.

In Plano, school officials sent e-mail alerts to parents with students in six different elementary and middle schools last week. Police say there have been six cases of suspicious individuals approaching children since Jan. 1.

While the cases don’t appear to be related, parents still worry. Some say they won’t be letting their kids walk home alone anymore.

“A good citizen just stopped to help a child in need,” Hostin said. “That’s a great thing about being in Mansfield; it still has a small-town community where people intercede when they need to.”