Windows 10 Mobile users on the Insider program in the Fast ring can download an update to Microsoft's GroupMe which adds video search features.
The new 126.96.36.199 beta version lets Insiders search for videos in the same way a previous beta update added support for JPG and GIF search inside the group messaging app. We will note that the videos themselves don't actually play inside the app itself. Rather, they open in the Microsoft Edge web browser.
We will again point out this GroupMe beta app is just for Windows 10 Mobile users in the Insider program on the Fast update ring. Regular Windows 10 Mobile users won't see these features in their GroupMe app version.