Police agencies in North Texas said Monday they are reporting varying levels of success and setbacks with so-called "safe exchange zones" for transactions from popular buy/sell apps.

The assessment comes after the murder on Friday of a teenager in Lancaster who tried to purchase a phone through the "5miles" app.

It marked the fourth homicide tied to buy/sell apps in North Texas over the last two years.

Lancaster PD says Gerard Cage, 18, was shot multiple times in the 1400 block of Rockbrook Street and later died at hospital.

Monday produced no new releasable leads according to Lancaster detectives, but did shed more light on the city's preparedness for safely facilitating buy/sell transactions.

The city of Lancaster confirmed to WFAA it does not have a designated "safe exchange zone" yet, saying the city is still working on improvements to its surveillance system before starting one.

"Residents are welcome to meet in front of or inside the Police Department lobby," the city said in a statement.

News 8 asked several North Texas police departments about the safe exchange zones Monday and found some departments touting their usefulness, while others don't use them at all.

The Dallas Police Department says it has not created safe exchange zones yet, despite the Dallas city council giving the green light to implement the program one year ago at its seven police substations.

Dallas saw two murders in 2016 from popular resale apps "offer up" and Dallas-based "5miles" app.

In October 2016, 42-year old Martha Teran was shot and killed trying to sell an iPhone7 in the parking lot of Medival Times in Dallas. Her killing came just three months after Daniel Ruiz, 20, was gunned down trying to sell a phone not far from Skyline High School.

In December 2016, Arlington Police say two suspects used "5miles" app to lure a mother to Target under the guise of selling jewelry. Both suspects didn't show up but instead followed April VanCleave home and shot her. An arrest was made in February 2017.

Arlington Police created its "safe exchange zone" in 2016, but reported Monday the program has had mixed results.

"Our detectives say we are still seeing an increase of people being victimized by selling on offerup, 5 miles, Craigslist you name it," Lt. Christopher Cook said. "

"We know people are utilizing it but unfortunately you still have that segment of the population that is still kind of trusting other individuals and meeting them offsite," Lt. Christopher Cook said. We still have a lot of our robberies occurring at nighttime unlit places and untraveled locaitons."

"From that measuring stick, we've still got a lot of work to do."

Fort Worth and Grapevine Police both reported their safe exchange zones are in still in operation and used frequently.

"5miles" app provides a comprehensive list of updated cities across the U.S. that offer safe-exchange zones.