Charoensri Chaikhat, chairwoman of the Phayao Women's Network, said on Wednesday that there have been many reports of Thai women being scammed by foreign men they met on Facebook.
"On Facebook, you cannot tell the true identity of a person on the other end because the person can manipulate photos and use a false name," Mrs Charoensri said.
She said a woman in northern Thailand was recently lured into having sex with a Nigerian man she met on Facebook. The man also stole valuables from her.
"I've also experienced a similar thing. A man who said he was French wanted to add me as a friend on Facebook, but I rejected him because I don't know him," Mrs Charoensri said.
She said Thai women, whether teenagers or adults, should exercise discretion when using social networking sites. They should not post personal information, such as identification card numbers and bank account numbers, because they could be seen by online criminals, she added.