The trial has begun for three teenage girls facing a total of 74 charges related to an alleged teen prostitution ring in Ottawa, revealing a bigger investigation than previously thought.

Last June, police in Ottawa and Gatineau arrested and charged the three accused with allegedly using social media to lure seven girls between 13 and 17 years of age to a home at a Walkley Road community housing project in southeast Ottawa.

That is also where one of the accused lived, neighbours said.

The Crown said Monday the accused may have started trying to recruit other girls as early as November of 2011, six months before their arrests.

Victims lured with party invite

The victims were allegedly invited online to a physical location with promises of a sleepover or party, and encouraged to drink or smoke marijuana once they were there. One was allegedly drugged with ecstacy.

They were then allegedly taken in taxis to the homes of men who would pay as much as $400 to have sex with them. The Crown said if they resisted, the accused pimps would beat them.

Two of the accused girls were 15 and the third was 16 at the time of their arrests, police said. The three accused, each represented by a different lawyer, are expected to testify at the trial.

A fourth accused, also a young woman, was mentioned in court Monday for the first time. Details are scarce, but the Crown said she will be tried separately.

One of four accused "johns," who are facing a charge of sexual assault related to the prostitution ring, is also expected to testify.

Facebook messages, tweets

The Crown said its evidence includes Facebook messages and tweets that correspond to the incidents, along with nude or semi-nude photos seized from a cellphone that were allegedly used to market the victims.

Neither the victims nor the accused can be named due to provisions of the Youth Criminal Justice Act.

The 74 charges — including human trafficking, procuring for prostitution, abduction, forcible confinement, robbery, sexual assault, assault, uttering threats and printing and publishing child pornography — are related to three separate incidents in 2012: one between May 16 and 19, another on May 30 and a third on June 3.

Police have said they don't believe the accused girls had any guidance from an adult.

The trial, expected to last about four weeks, will include testimony from detectives, victims and the mother of one of the accused.

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Romanian students dressed as caged brides attend an event to raise awareness to the risks of human trafficking and sexual exploitation faced by young girls lured by the prospect of a better paying job abroad, in Bucharest, Romania, Saturday, Nov. 19, 2011. (AP)