MySQL, can't find MYD files on OS X, MAMP
MyISAM still uses .MYD and .MYI.
The only way you can see .frm  files only and no other table file would be this:

All tables are using InnoDB
innodb_file_per_table disabled (all table data would be inside ibdata1)

If you can log into MySQL, run this
SELECT IFNULL(engine,'total') engine,(data_length+index_length) tblsize
FROM information_schema.tables WHERE table_schema NOT IN
('mysql','information_schema','performance_schema')
GROUP BY engine WITH ROLLUP;
SELECT @@global.innodb_file_per_table;
SELECT @@global.datadir;
SELECT table_schema,table_name,engine,(data_length+index_length) tblsize
FROM information_schema.tables WHERE table_schema NOT IN
('mysql','information_schema','performance_schema')
ORDER BY engine,table_schema,table_name;

These will fully reveal your data and storage engine situation.
UPDATE 2015-05-01 19:48 EST
Based on the output of the queries I gave you

4KB worth of MyISAM
16KB worth of InnoDB
@@global.innodb_file_per_table = 0 means all the table and index space for your InnoDB tables are inside /Applications/MAMP/db/mysql/ibdata1

To see your MyISAM tables, run this:
SELECT table_schema,table_name
FROM information_schema.tables WHERE table_schema NOT IN
('mysql','information_schema','performance_schema')
AND engine='MyISAM';

To see your MEMORY tables, run this:
SELECT table_schema,table_name
FROM information_schema.tables WHERE table_schema NOT IN
('mysql','information_schema','performance_schema')
AND engine='MEMORY';

To see your InnoDB tables, run this:
SELECT table_schema,table_name
FROM information_schema.tables WHERE table_schema NOT IN
('mysql','information_schema','performance_schema')
AND engine='InnoDB';

To get the count of the tables by engine:
SELECT table_schema,COUNT(1) table_count
FROM information_schema.tables WHERE table_schema NOT IN
('mysql','information_schema','performance_schema')
GROUP BY engine;

To get the count of the tables by engine in each database:
SELECT table_schema,engine,COUNT(1) table_count
FROM information_schema.tables WHERE table_schema NOT IN
('mysql','information_schema','performance_schema')
GROUP BY table_schema,engine;