Unexpected Return from Function

I have a FUNCTION:

CREATE FUNCTION get_responsible(text)
RETURNS TEXT AS '
DECLARE responsible_list text; my_record RECORD;
BEGIN FOR my_record IN SELECT login FROM employee WHERE id IN (1,2) LOOP   responsible_list := responsible_list || '',
''my_record.login; END LOOP; RETURN responsible_list;
 
END;
' LANGUAGE 'plpgsql';

The employee table is such:

id | login
-------------
1  | anthony
2  | mary
-------------

I expect the SQL statement "SELECT get_responsible('1,2')" to return
something like so:

get_responsible
---------------
anthony, mary
---------------

But instead I receive:

get_responsible
---------------

---------------

If I get rid of the concatenation, like so:

CREATE FUNCTION get_responsible(text)
RETURNS TEXT AS '
DECLARE responsible_list text; my_record RECORD;
BEGIN FOR my_record IN SELECT login FROM employee WHERE id IN (1,2) LOOP   responsible_list := my_record.login; END
LOOP;RETURN responsible_list;
 
END;
' LANGUAGE 'plpgsql';

I receive last result (for id = 2), like so:

get_responsible
---------------
mary
---------------

The SELECT statement itself runs fine, so I know it is returning two
records.

Also, the reason I am passing a 'text' datatype to the function, is
because I'd ultimately like to have the "WHERE id IN" statement to be
dynamic, like so:

CREATE FUNCTION get_responsible(text)
RETURNS TEXT AS '
DECLARE responsible_list text; my_record RECORD;
BEGIN FOR my_record IN SELECT login FROM employee WHERE id IN ($1) LOOP   responsible_list := my_record.login; END
LOOP;RETURN responsible_list;
 
END;
' LANGUAGE 'plpgsql';

If anyone can help me with this, I'd be much appreciative.  I've been
trying combination after combination of things to try and resolve this
for the past 6 and a half hours.

Thanks,

Anthony "pulling his hair out" Bouvier