It's located at https://www.facebook.com/. You cannot access the People search bar on a mobile device. This option is in the group of blue links near the bottom of the sign-up page. It's a white bar on the far-right side of the page with "Search for people" written in it. Make sure they're spelled correctly. If you've tried this method before, you can also try variations of their name (e.g., "Jack" for someone usually named "John", "Vicki" for "Victoria", etc.). You may first need to verify that you aren't a spam bot by typing in a code as it is displayed on-screen. It's right of the search bar. This will search Facebook for all profiles matching your entered name. If you don't see the profile of the person for whom you're searching here, you might want to try a Google search just to be sure. If you do see the profile here, you won't be able to click on it; however, you'll at least know that the person in question has a Facebook account.

How would you rephrase that briefly using Vietnamese?
Vào trang chính của Facebook trên máy tính tại https://www.facebook.com/. Kéo xuống và nhấp vào đường dẫn People. Nhấp vào thanh tìm kiếm. Gõ họ tên người dùng. Nhấp vào Search (Tìm kiếm). Xem kết quả tìm kiếm.