Police are warning young people to be wary when using social media and online apps to meet after a 39-year-old man was charged for the second time in three months with sexual interference against a child under 16.

A 15-year-old girl went to police in April after earlier meeting up with a man in south Calgary who identified himself using an alias. The pair had initially met through an app called Whisper, which allows users to send and receive messages anonymously. The man invited the girl to his residence in Woodbine, where police allege he sexually assaulted her.

Officers were able to find out his real name and an investigation was launched.

In August, Ian Patrick Wilson, 39, was charged with one count each of sexual interference with a child under 16 years, sexual assault and luring via a telecommunications device.

Then in October, another 15-year-old girl went to police to say she had met a man through the same app, who had identified himself using a different alias.

The man invited the teen to his residence in February, where police allege he sexually assaulted her.

She again went to his residence in March, where police allege he again sexually assaulted her.

Police identified the man's real name and the second girl was able to identify a suspect through distinctive tattoos in a photo lineup.

On Wednesday Wilson was again charged with sexual interference with a child under 16 years, sexual assault and luring via a telecommunications device.

Calgary police Staff Sgt. Melanie Oncescu. (CBC)

At a press conference Thursday, Staff Sgt. Melanie Oncescu, of the Calgary police child abuse unit, said Wilson was known to police.

Oncescu encouraged parents to be aware of the apps and websites their kids are using and who they are interacting with online.

"It's really important for parents to sit down, have honest conversations with their children, talk about what's safe practices, what apps are appropriate and what they share in social media," Oncescu said.

Calgary police encourage all victims of sexual assault, or any crime, to report it by calling the non-emergency line at 403-266-1234, by going to any district office or by calling Crime Stoppers at 1-800-222-8477.