Touch to Search, which enables users to highlight a single word or line of text in the mobile version of Chrome and instantly search for that text in Google, is pretty neat. It was introduced in the beta build of Chrome for Android version 38 way back in March of last year. But in the latest versions of the app (including the standard release), it's been curiously absent for many users.
If Touch To Search is gone for you and you'd like it back, I have good news. Re-enabling the feature is as easy as flipping a switch in Chrome's digital toolbox, the flags page. Head to chrome://flags page by entering it into the URL field, then search for the option called "Enable Contextual Search" (you can use the "Find in page" option to search for that, or "#contextual-search"). Enable that option, then close Chrome and re-open it.
Once you've launched the app again, go into the Settings menu and tap "Privacy." There's an option at the bottom of the page called "Touch to Search." Set that to "On," and you're good to go. The feature should now be available on all web pages. This should work for Chrome stable, beta, and dev. Enjoy!