Hi,
How to say this in Turkish "Keep up your good work".

Regards,
Scott 

From the tureng  online dictionary I found

aferin böyle yapmaya devam et

aferin means well done!, devam et means continue, böyle means like that, 

and literally well done, continue to do like that.

Have a look at the second meaning when you click on the dictionary link. If a Turk, who didn´t know English, wrote that to someone, it may really confuse them. 

aferin, iyi çalışmana devam etsene would be my attempt as a learner, but wait for a Turk to comment on this.