Statistics don't tell the whole story but can be helpful to get a general idea of what is going on.  Missionary Dwight Martin collects data on the Thai church and recently released the data on Thai church growth in 2009.  Here is an excerpt from his report, along with some links for more information:

"At the end of 2009 there are 339,048 Christians, which is 0.54% of the total population.  Even though this is a very small percentage, the good news is that the percentage of growth is seven times faster than the biological growth rate of the country.  The number of churches continues to grow as well.  There were 170 new churches started last year (2009). 
 
The need is still great in Thailand.  Over 47% of the sub-districts in Thailand have no Christian presence at all. This means there are 21,814,049 (about 1/3 of the population) people who have very little opportunity to hear the Gospel Message.  Please pray that God's word will penetrate this whole nation.

 
If you are interested you can download the complete PowerPoint presentation by clicking here for the English version and clicking here for the Thai version.  The presentation has many more facts and details that you may find of interest.
 
You can also find maps (in Thai) of the Christian population and presence for every province in Thailand by visiting http://www.thaicrc.com and clicking on the icon that shows the map of Thailand."

In the Powerpoint presentation linked above, you'll see a page for the "My Hope Thailand" project, where there is a statistic for number of "salvations" (or number of people who prayed the sinner's prayer as the result of the My Hope evangelism project). Regular readers of this blog will know the serious objections that I have to the theology and methodology of the sinner's prayer.  However, the "salvations" reported as a result of the My Hope project are NOT included in the 2009 Thai Church statistics.  The church growth numbers reported above are based upon church membership, not upon saying the sinner's prayer.

How many of the people who made a "decision" for Christ during My Hope and actually go on to become church members (and hopefully truly converted Christians) remains to be seen. But speaking charitably, My Hope represents widespread sowing of the Gospel in Thailand and the fact that many Thai people have been exposed to some form of the truths of Christianity.

In any case, since the church growth numbers above are based on church membership and not the sinner's prayer, they are thus a somewhat accurate way to gauge actual growth of the visible church in Thailand.  And the church in Thailand IS growing!  Praise God! Christ is building His church (Matt 16:18). 

May the Lord continue to growth His church not only in numbers but also in depth and maturity, purifying a people for Himself from among the Thai.