A woman who posed as a teenage boy to groom girls as young as 13 online and travelled around the country to sexually abuse them has been jailed for eight years.

Some of the vulnerable girls targeted by Gemma Watts, 21, were so traumatised by their ordeals and a sense of betrayal that they have self-harmed or tried to kill themselves.

Watts, who used the alias “Jake Waton”, was jailed for seven offences involving four girls but detectives believe she may have groomed as many as 50 teenagers and are appealing for other victims to come forward.

Officers said many victims would only realise they had been tricked by Watts now she had been jailed and her case widely publicised.

Watts, who lived at home with her mother in Enfield, north London, shared skateboarding videos and flattered victims with complimentary messages, calling them “babe” or other pet names.

When she met victims in person, she tied her long hair into a bun and wore a baseball cap, baggy jogging bottoms and a hoodie to convince the girls she was Jake. Watts was so convincing that she even spent lengthy spells as Jake with some of the girls’ parents.

After she was arrested, Watts told police she saw it as a game and claimed: “I was only trying to cheer them up.”

The judge, Susan Evans, said there was significant planning behind Watts’s campaign and elements of her behaviour were predatory. All the girls she targeted were vulnerable and some had previously been bullied and had low self-esteem.

The judge said it was worrying that even after being warned by police, Watts continued to groom and meet girls. “It seems that nothing deterred you,” she said.

Evans accepted Watts had a low IQ, was immature, had issues about her own sexuality and had no previous convictions. But she said some of the abuse was sustained and some victims suffered severe psychological harm.

Her victims included a 14-year-old from Hampshire who had suffered bullying and mental health problems.

When the girl questioned Watts over her breasts, she said they were “man boobs” that had appeared when she was overweight.

The girl found real images of Watts dressed as a woman but Watts claimed she had been experimenting with wearing female clothes. Watts even stuffed rolled-up socks into her shorts to trick the girl into making it appear that she had a penis.

The court was told Watts became increasingly violent towards the girl, trying to push her into the path of a vehicle and once threatening her with a knife.

In her victim impact statement, the teenager said her “heart exploded” when she found out Jake was an adult woman. She said she had loved Jake and thought she could tell him everything.

Since the truth emerged, the girl said she had cut herself and been admitted to hospital after taking tablets. “She’s in my head,” the victim said. “What she has done to me is gross, horrible.”

Watts also met up with another 14-year-old girl from Surrey while posing as Jake. The girl was excited at receiving her first “proper” kiss. The youngest victim identified so far was just 13.

While police investigated Watts, she was ordered by a court not to approach anyone aged under 16 but she breached the order within days.

Speaking outside court, DC Phillipa Kenwright of the Metropolitan police said: “I think there will be further victims, who were in a relationship with Watts, who will now realise she is a woman. I think there could be 20 to 50.”

PC Nicola Benson, from Hampshire constabulary’s missing and exploited team, said: “The level of manipulation and deceit used by Watts to snare her victims in this case was truly shocking.”

Watts admitted one offence of assault by penetration, three other sexual assaults and three counts of meeting a child after sexual grooming.

• In the UK and Ireland, Samaritans can be contacted on 116 123 or email jo@samaritans.org or jo@samaritans.ie. In the US, the National Suicide Prevention Lifeline is 1-800-273-8255. In Australia, the crisis support service Lifeline is 13 11 14. Other international helplines can be found at www.befrienders.org.