I have one specific string, such as \"123abcd\" for example but I don\'t know the name of the table or even the name of the column inside the table on my SQL Server Database
Here are couple more free tools that can be used for this. Both work as SSMS addins.
ApexSQL Search – 100% free - searches both schema and data in tables. Has couple more useful options such as dependency tracking…
SSMS Tools pack – free for all versions except SQL 2012 – doesn’t look as advanced as previous one but has a lot of other cool features.