The virus has increased fourfold in Sunderland, Durham and Teesside, the areas of Britain where the website is most popular.
Medics believe Facebook and other social networking sites make it easier for strangers to meet multiple partners for casual sexual encounters.
Professor Peter Kelly, director of public health in Teesside, said staff had found a link between the websites and the rise in cases, especially among young women.
‘Syphilis is a devastating disease. Anyone who has unprotected sex with casual partners is at high risk,’ he said.
‘There has been a fourfold increase in the number of syphilis cases detected with more young women being affected.
‘I don't get the names of people affected, just figures, and I saw that several of the people had met sexual partners through these sites.
‘Social networking sites are making it easier for people to meet up for casual sex.
‘There is a rise in syphilis because people are having more sexual partners than 20 years ago and often do not use condoms.’
In Teesside there were 30 recorded cases of syphilis last year, but the true figures are expected to be much higher.
Syphilis cases in Britain fell due to the widespread use of condoms in the 1980s and '90s.
It can cause serious heart, respiratory tract and central nervous system damage.
But Health Protection Agency figures revealed there were 4,000 cases nationwide last year. And in 2008 there were 3,588 diagnosed cases.
The highest rates are in women aged 20 to 24 and men aged 25 to 34.
Research has shown that young people in Sunderland, Durham and Teesside were 25 per cent more likely to log onto social networking sites than those in the rest of Britain.
Studies have shown that adults are more likely to indulge in risky sexual behaviour with partners they meet on the internet.
Facebook denied members typically use the site to set up sexual encounters with strangers.
A spokesman said: 'While we have not had an opportunity to read this research, Facebook is not the place to meet people for casual sex, it is about connecting and sharing with your existing friends.'
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