While all the participants in a study had social problems such as loneliness, none had previous episodes of psychosis or drug abuse.
"As internet access becomes increasingly widespread, so do related psychopathologies," Lead researcher Dr Uri Nitzan said.
"Some patients are harmed by these social networking sites, which can attract those who are lonely or vulnerable in their day-to-day lives or act as a platform for cyber-bullying and other predatory behaviour," Nitzan said.
Focusing on Dr Nitzan's patients, researchers found they had all sought refuge from a lonely situation and found solace in intense virtual relationships.
Although these relationships were positive at first, they eventually led to feelings of hurt, betrayal and invasion of privacy.
Dr Nitzan, of Tel Aviv Univers-ity's Sackler Faculty of Medicine and the Shalvata Mental Health Care Centre, said: "All the patients developed psychotic symptoms related to the situation, including delusions regarding the person behind the screen and their connection through the computer."
The study is published in the Israel Journal of Psychiatry and Related Sciences.