Police have launched a murder investigation after the discovery of a body believed to be a missing 14-year-old girl in south Wales.

The body was found in Duffryn Park in the town of Blaina, Blaenau Gwent at approximately 10.10pm on Monday, the police force said in a statement.

No formal identification has taken place, but police said the family of Lilly, a 14-year-old girl who was reported missing on Saturday, had been informed. The force has urged anyone with information related to the case to come forward.

DCI Steven Thomas said: “We understand that this will cause distress and concern amongst our communities. We have a large police presence in the area at this time as enquiries are ongoing to establish the circumstances of the death.

“Our officers are here and available for you to speak to. We encourage anyone with information to please speak with us or you can contact us on the usual channels.”

Gwent police launched a media notice for help finding Lilly on Monday afternoon after she was last seen on Blaina’s High Street at approximately 6.50pm on Saturday. Wales Online reported that two young people looking for her found the body.

Members of Lilly’s family also issued frantic social media appeals to locate her. “[She] went out at 6.30 and hasn’t come home – very much out of character,” her aunt, Zoe Jones, wrote. “Lilly please come home my girl, I promise you’re not in any trouble … we just want you home.”

Lisa Catherine Winnett, a local councillor, said the community was “devastated” by the news. “My thoughts and prayers are with Lilly’s family at this devastating and awful time,” she said. “I hope police work promptly now to find the perpetrator.

“We are a close-knit community here in Blaina and the impact this has had on all of us is immense. Since Lilly was reported as missing there has been extensive searches by family, friends and members of the community. On Monday, police had drones searching and helicopters.

“I would like to thank everyone involved in the searches. This outcome is totally unimaginable for us all.”

Agency pictures showed a police cordon and heavy police presence in the area on Tuesday. Forensic investigators and emergency services teams have been working in the Duffryn Park area since Monday night.