Telling a newcomer they should have ‘read the FAQ’ or ‘searched for previous questions’ on the topic before they posted is a bad idea.
In fact, it’s the most sure-fire way to guarantee he won’t participate again.
Two options. One, remove the post and answer it by e-mail rather than publicly rebuke him.
Second, and better, highlight how it’s about time this topic came up again, identify any possible new information on the topic, reference previous discussions on the topic, and any useful link in the FAQ.
Perhaps invite other experts in that topic to update their views?
Your members should feel terrific about asking their first question, not foolish.