The default trace records which login is responsible for file autogrowth. This sometime shows as sa, for example during some system operations, but it is worth a try.

Here's the script I use:

use master;

set nocount on;

declare @path sql_variant

select @path = value

from ::fn_trace_getinfo(0) i

join sys.traces t on t.id = i.traceid

where t.is_default = 1 and i.property = 2

select df.StartTime,

e.name,

df.DatabaseName,

case when df.ApplicationName like 'SQLAgent%JobStep%'

then isnull((select name from msdb..sysjobs where job_id = CONVERT(uniqueidentifier, convert(varbinary(16), substring(df.ApplicationName, charindex('(Job', df.ApplicationName) + 5, 34), 1))), df.ApplicationName)

else df.ApplicationName end AppName,

df.LoginName,

df.SPID,

df.Duration,

df.EndTime,

df.FileName,

df.TextData,

df.IntegerData

from ::fn_trace_gettable(convert(nvarchar(255), @path), 0) df

join sys.trace_events e ON df.EventClass = e.trace_event_id

where e.category_id = 2

order by df.StartTime desc

If the default trace file has rolled over, modify the first bit to look at an older file.