The app Posts (Messages) of OS X for years it has been criticized a lot by users, and with good reason: it is well left by Apple. But at least one of its search failures can still be "improved" through external solutions.
In mid-2013 we gave the tip of Chatology here on the website, which remains superb and working well. But it is not very cheap, so it is worth another tip even if simpler.
THE MessagesHistoryBrowser it is another utility that aims to improve the search within the Messages app, allowing you to browse all of its history (or only for certain periods), save chats in text files and also find images sent in them.
The first time it is run, its entire message base is imported which, depending on its size, can take a while. From there, he only pulls what's new again.
Free, created by Guillaume Laurent, MessagesHistoryBrowser requires OS X El Capitan 10.11 or higher. It can be downloaded here (ZIP), as it is not on the Mac App Store.
(via Mac Kung Fu)