Some Pechenegs and Turkmens served under the Byzantines. As far as I'm aware of, Hungarians also made early use of Cumans. Bulgars were possibly a factor during their migration to Macedonia as well.

Turkic mercenaries were mostly present in the Balkan area. Aside from Poland and Russia employing Nogai and Tatar mercenaries from time to time, I am yet to see a single mention of them being used anywhere else in Europe.