That's according to a survey of most state medical boards that license and discipline doctors.
Most boards said they'd received at least one complaint about unprofessional online behaviour; 25 per cent had received more than three complaints.
The most common violation was asking patients out online. Others were prescribing medicine and overstating medical credentials online.
More than half said complaints led to serious punishment including revoking medical licenses.
The survey appears in Wednesday's Journal of the American Medical Association. Violations occurred over about 10 years.
The Federation of State Medical Boards is considering adopting professional guidelines for doctors' use of social networks and other online behaviour.