Recruiters, do you ever catch current employees job-hunting?
Recruiters of HN, have you ever found out a current employee is applying to other jobs via your recruiting network? Or perhaps a LinkedIn setting tipped you off.
Is there any sort of SOP for this? Do you tell the employee’s manager as a heads up, or simply ignore it and keep it to yourself?
Not a recruiter. You ignore it and keep it to yourself. Full stop. People look for jobs for any number of personal reasons.
Keep it to yourself. What is this schoolyard tattle-tale behavior? Employees have a right to job hunt. Additionally, interviewing is a skill and people should do practice interviews when they don't want a new job and for jobs they don't want, so that they can be prepared when one they do want comes up. And they should do that because assholes like you do nothing to help them get those jobs and then take a fat slice on top of their paychecks.
Passing such information on would be very unethical.