Conferance on Gagauz Turkish (Gagavuz Türkçesi) gives some concrete numbers on population, geographic extent

Here's a short but informative article on the Gagauz, the majority Orthodox Christian but (nearly) Turkish-speaking group concentrated mostly in Moldova.

The Turkish Language and Culture Faculty from Near East University (Yakın Doğu Üniversitesi, YDÜ) held a conference on Gagauz Turkish. There the Turkolog Erdoğan Saracoğlu said that the large majority of the Christian Turk Gagauz live in Moldova, while others live in Ukraine, Russia, East Kazakhstan, Bulgaria, Romania, Greece and Macedonia. According to a USSR census in 1989 there were a total of 197,164 Gagauz in the country (which included Moldova at the time). According to Saracoğlu there are a total of up to 5,000 Gagauz in Bulgaria, and small groups of Gagauz in Kazakhstan and Central Asia who fled Bessarabia from 1908 to 1914. Saracoğlu said that the total Gagauz population is about 500,000.