You cannot, i repeat, you CANNOT, use "נאבדו" that's street hebrew and is not a real word. The correct way to say it is אבדו לי התכשיטים. I will report this question and hope the mistake will be fixed soon.
I would say התכשיטים שלי אבודים but not in the sense that I can't find them, only in the sense of "they are broken beyond repair". Otherwise I agree with bar_an, I would use a verb form, אבדו, נאבדו, or more likely, הלכו לאיבוד.
"נאבדו לי התכשיטים" is not Hebrew. If you wish to say "my jewelry is lost, usually you'll say" התכשיטים שלי הלכו לאיבוד". Usually you don't use the" אבודים" adjective in this situation.