list non alphanumeric

Hi

Firstly let me mention I am a noob to postgres,DB and sql anyway, I have a column with First names and need to list names that have non-alphanumeric characters in them like + or * and the list goes on. I did google a bit and tried:
select * from TABLE where first_name not like '%[a-z0-9]%';

However the above shows all the entries in that column and if I change it to Like, which should show all the entries it shows nothing.

e.g of my goal:

Column
Bob
Jane+
Harry*
John
Mike
Larry

My query should output

Jane+
Harry*

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