I am working in Postgres 9.4. I have a table and index like this:

                                                  Table "public.title"
                 Column              |          Type           |                     Modifiers                      
    ---------------------------------+-------------------------+----------------------------------------------------
     id                              | integer                 | not null default nextval('title_id_seq'::regclass)
     pty_addr                        | character varying(1000) | not null

I have a GIN index on the `pty_addr` column:

    "title_pty_add_15f367_gin" gin (pty_addr)

My query is this:

    EXPLAIN ANALYZE SELECT * FROM "title" WHERE  pty_addr LIKE '%FOO%';

This query is performing a sequential scan, taking 1.2 seconds:

                                                      QUERY PLAN                                                   
    ---------------------------------------------------------------------------------------------------------------
     Seq Scan on title  (cost=0.00..193271.60 rows=599 width=4446) (actual time=1.191..1220.640 rows=7945 loops=1)
       Filter: ((pty_addr)::text ~~ '%FOO%'::text)
       Rows Removed by Filter: 3592055
     Planning time: 0.330 ms
     Execution time: 1220.992 ms

Why isn't this query using the index?