Foods added by members are often wrong and/or missing key pieces of info (eg some people enter calories only), so they don't come up by default. It's best to stick with the main database normally.
There are two options - searching foods entered by other users, and seaching manually entered foods (yours). You may not have had the right one selected when trying to find that other member's food again.
If you manually enter foods and want to share them so that others can find them when they select "foods shared by other members" then you need to specify you want to share those. I think that's on the Favorites tab.
Deb, in New Zealand