Thirteen men, all of Somali origin, have been convicted of the systematic sexual abuse of vulnerable girls as young as 13 in Bristol and officers are investigating claims against 49 other suspects.

The victims, some of whom were in local authority care, were groomed and passed around by their abusers – often for money – and assaulted in homes, parks and a hotel.

One of the girls was raped at age 13 on the same night by three different men, including a stranger, and thought her life would be in danger if she went to the police.

Another girl was sexually exploited after a local authority outside Bristol set her up alone in a flat at the age of 16 in a deprived inner-city neighbourhood although she had been described as having the emotional development of a three-year-old.

Within hours of arriving, she was spotted by drug dealers who set up a base in her new home and forced her to work as a prostitute. The abuse continued for months even after she told care workers about what was happening; the girl’s 14-year-old sister was subsequently raped during a visit.

A serious case review will look at the case and examine whether more should have been done to protect the girls. Ten girls came forward to make allegations about the 13 men but Avon and Somerset police said they were actively pursuing nine other investigations across the force area, involving suspects from various communities and ethnic backgrounds. The Guardian has learned that 49 suspects and 48 victims are involved in these investigations.

Detectives expressed concerns that hotels were being used for exploitative sex parties and the police have worked with the Premier Inn chain because one of the most savage attacks took place at one of its hotels.

Avon and Somerset police have said the case has similarities with large-scale child exploitation cases in places such as Oxford and Rochdale, where men of Asian heritage have been found guilty of abuse. But this the first time members of the Somali community have been found guilty of such crimes.

Police said they were aware that the case could prompt hate attacks.

Six of the men, most of whom are in their early 20s, have begun jail terms for offences including rape, paying a child for sex and arranging or facilitating payments for the sexual offences of a child. Another seven – one of whom appeared in both trials – were convicted this week of offences including rape, causing or inciting child prostitution, sexual acts with children and trafficking.

Some of the offenders were members of a drugs gang that sold heroin and cocaine in Bristol. Others were well-educated men with good prospects. The lifting of reporting restrictions on Thursday means that the story can be told for the first time.

The case has caused huge concern in Bristol. Teachers have been briefed and some teachers at inner-city schools have claimed it is not uncommon for schoolgirls to boast about being paid for sex.

It has also sent shockwaves through the Somali community in Bristol. Muna Abdi, chair of the Bristol Somali Forum, said the men had committed “evil acts” that the Muslim community utterly condemned.

A joint statement from the Bristol Somali forum and the Somali Resource Centre said: “The Somali community is law-abiding and values law. The shock of this case, like a thunderbolt, has struck at the heart of our proud and law-abiding community in a way that is impossible to describe.”

Children’s charity Barnardo’s continues to care for some of the victims. Hugh Sherriffe, director for Barnardo’s in the south-west and Midlands, said the case was the “tip of the iceberg” and such abuse was going on across the UK and demanded more efforts to stop it.

Detectives began investigating last year after the 13-year-old was raped by three men on the same night just before Christmas 2012.

A group of young men had gathered in a room at a Premier Inn in Bristol. One of them, a 22-year-old drug dealer called Said Zakaria – also known by his street name Target – was tasked with the job of finding girls to “party with”. Zakaria went off to pick up the 13-year-old, who can only be identified as Complainant One (C1).

Rather than bringing her straight to the hotel, Zakaria first dropped her off an inner city flat where she was raped by a stranger. He took her on to the Premier Inn where he raped her twice and another man raped her once.

By the time C1 was picked up by Zakaria, she was accustomed to abuse, having been groomed by one of Zakaria’s friends, Mohamed Jumale, since the age of 11. She lost her virginity with him under a bridge on a cycle way and he coerced her into having sex with other men, telling her this was his culture.

After police began investigating, other teenagers came forward to report that they had been abused by young men of Somali origin in flats, parks, and in the disabled toilets in a shopping centre.

In January last year – the month after the Premier Inn attack – a 16-year-old girl who can only be identified as Victim A was placed by a local authority outside the area alone in a Bristol flat. She was said to be scared of the dark and craved company. However, she was given a little supervision but left to cope alone for 22 hours a day.

One of the first people she met when she ventured out alone was Zakaria. She asked him if he could get her “weed” and they began chatting. Within hours, the drugs gang Zakaria was part of was setting up shop in A’s flat.

Over the next months they used it as a safe house to stash and prepare heroin and cocaine before selling it.

They also began to sexually abuse A. One gang member acted as her pimp. He would stand guard as she had sex with men. Together they could make £300 a day from five or six clients. Victim A grew fond of some of her abusers (her social worker compared it to a kidnap victim falling for her kidnappers). She said she was glad to please the men and felt “part of something”.

In May last year, her 14-year-old sister, who was also in care and had run away, was raped at the flat. Police arrived looking for her and heard a knocking from a cupboard under the sink. The girl was dressed only in her underwear. She was crying and make-up was running down her face. “They made me do stuff,” she said.