Jewish scholars tell us that as many as 20% of first century Israel may have accepted Jesus as the Messiah. We know that three thousand came to the Lord on the Feast of Pentecost (Acts 2:4) and shortly afterwards another 5,000 men plus any women and children became believers (Acts 4:4). Acts 6:7 then records that a large number of priests became obedient to Christ.
Many years later when Paul came back from his third missionary journey, probably around 60 AD, we read that the number of true Christians had already grown to tens of thousands - see Acts 21:20. The Greek word used in this verse is murias, which according to The New Thayer's Greek-English Lexicon of the New Testament, literally means;
"a ten-thousand; a myriad or indefinite number; an innumerable multitude; an unlimited number" (p.419).
See Luke 12:1, Acts 19:19 and Jude 14 for examples of the use of this word.
If there were already so many believers in 60 AD, there would be no places left between the 1870s and 1930s when the Jehovah's Witnesses say that the number of the 144,000 was made up. It would mean that even if we were only talking about 30,000 believers in 60 AD (and there would have been many more than that) only 60 people per year could have been saved up to 1935 - that is ridiculous and would mean that the sovereign power of God was severely restricted.
Surely then, the evangelical Biblical evidence shows that the teaching that there are only 144,000 believers who will be with Jesus, in heaven, is not true. This of course also means that one of the central teachings of the Jehovah's Witnesses is false.
ANOTHER WAY OF LOOKING AT IT
There is also another way of looking at it as a former Witness, Phil Mawson wrote a number of year's ago:
The Jehovah's Witnesses believe that only 144,000 people are in the New Covenant. What does the Bible say?
Galatians 4:22-31 mentions how Abraham had two sons, one by Hagar the bondwoman and another by Sarah the free woman. These sons being Ishmael and Isaac respectively. Verse 24 states clearly that these two women,
"stand as symbolic drama, for these women mean two covenants." New World Translation, Watchtower Bible & Tract Society.
Verses 24 & 25 tell us that Hagar symbolises the Old Law Covenant from Sinai, while in verses 26 & 27 Sarah stands for the New Covenant and the Jerusalem above our [i.e. the Christian's] mother. In verse 27, Paul quotes from Isaiah 54:1 where Jehovah God is married to the nation of Israel via the Law Covenant. Compare also Jeremiah 3:14, 31:32.
Thus the barren or desolate woman which represents the New Covenant, has "many more children" [NKJV] or "more numerous" [NWT] than the woman who has the husband. The latter representing the old Law Covenant between Israel and Jehovah.
It is evident that this old Law Covenant brought forth millions of children from the time of Moses to John the Baptist - Matthew 11:13. And we read here that the New Covenant would bring forth many more than this; yes they would be "more numerous" as the NWT puts it. The New Covenant would comprise Jews and Gentiles, without any distinction, see Romans 3:22. Thus, it can be easily and Scripturally demonstrated that the New Covenant is made with millions of persons, and not just 144,000 as is taught by the Watchtower Society of Jehovah's Witnesses.