Natasha Randall was found hanged in her bedroom at her home in Blaengarw, Bridgend.
South Wales Police have been examining a computer used by the teenager, who was a member of social networking site Bebo.
A task force including police, schools and health workers are now investigating her death last Thursday.
The group was set up to create an action plan following the deaths of six young men in the Bridgend area over the past year.
It is thought there were some links between the seven young people who have now died.
Dale Crole, 18, was the first to kill himself. His body was found in a disused building in Porthcawl, South Wales, in January 2007.
The following month, 19-year-old David Dilling was found hanged near his home in Pyle, Bridgend. Thomas Davies, a 20-year-old friend of Dale and David, was also found hanged in February.
In August 2007, 17-year-old Zachary Barnes, of Wildmill, Bridgend, was found hanged. Last month, 20-year-old Liam Clarke, a friend of Dale Crole, was found hanged in a Bridgend park.
Earlier this month, 27-year-old Gareth Morgan, who knew Liam, was found hanged at his home in Bridgend.
Natasha, whose death was the seventh, left a message on her page on Bebo to Liam after his death, reading: "RIP Clarky boy!! gonna miss ya! always remember the gd times! love ya x. Me too!"
Messages have now been left on Natasha's own site, with one saying "RIP tash - can't believe you done it!" and another from Sadie James saying: "Heyaa Babe. Just Poppin In To Say I Let My Balloon Off With A Message On It, Hope You Got It Ok And It Made You Laugh Up There."
Liam's father, Kevin Clarke, 46, told the Daily Mail the deaths were "very strange".
He said: "We just don't know what this is about. It is very strange that there have been so many suicides in Bridgend and that they all seem to know one another.
"We don't know if it is some weird cult or copycat suicides or if they have had some bizarre pact to kill themselves."
A 15-year-old girl who knew Natasha tried harming herself the day after her death in nearby Pontycymmer.
Pupils at one local school have since been told to approach staff if they feel depressed.
Blaengarw councillor Carl Rees said: "There has been speculation about the visiting of suicide sites but there is no evidence for that.
"It is a shock. My condolences go out to the family of the 17-year-old. Obviously she is a young girl and it is such a shock.
"It is a shame what she did."
He added: "This is a small village and something like this is a talking point. When I was coming home last Thursday from shopping, police and ambulance cars were screaming past to the scene."
Superintendent Tim Jones, divisional commander of Bridgend Police, said: "We are currently investigating the circumstances surrounding the death of a 17-year-old girl in Blaengarw on Thursday, January 17 and will be reporting on this matter to the coroner.
"It is important to stress that at this time we have not established any direct links between the death of the 17-year-old female in Blaengarw on Thursday and a 15-year-old girl attempting to harm herself in Pontycymmer on Friday. However, they were known to each other, as you would expect in small neighbouring communities.
"One line of inquiry within the investigation is the examination of the computer of the 17-year-old girl, which is currently ongoing.
"The investigation will seek to establish the full circumstances surrounding these tragic circumstances and clearly communication between friends and associates is an important consideration.
"There is a growing trend for young people to communicate through telephone text messaging and also over the internet, whether it's email or within chatroom forums.
"This is all part of conducting a thorough investigation."
He said police were doing "everything possible" to support young people in the area, and added: "As part of our response to these incidents over the weekend we identified associates and friends of both girls, and CID detectives and neighbourhood policing teams spoke to many young people in Blaengarw and Pontycymmer and also visited parents.
"We felt we had a duty of care to inform parents of what had happened so they may speak to their children about these distressing incidents and provide any emotional support they deemed necessary.
"We have also worked closely with the children's services within Bridgend so that they may provide any additional specialist support they may be required.
"Sudden deaths at any age are tragic situations and the police see first-hand the devastation particularly the deaths of young people have on their family and the whole of the community.
"We at South Wales Police will continue to do everything possible to play our part in supporting young people and those in our communities who are affected by such tragedies."
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