God did tell us in the bible to pray for one another. But i have not seen any verses that God commands / tells us christians to ask help for prayer on dead saints.
What you say is true; I don’t recall any instances in the Bible where someone prayerfully addressed dead saints and asks them for help. However, in more general terms, there are some instances in the Bible, especially in the Catholic Bible, where someone other than God is prayerfully addressed and asked to do something:
Bless the Lord, O you his angels, you mighty ones who do his word, hearkening to the voice of his word! (Psalm 103:20)
Praise him, all his angels, praise him, all his host! (Psalm 148:2)
From the Song of the Three Young Men found in Daniel in Catholic Bibles:
Bless the Lord, you angels of the Lord, sing praise to him and highly exalt him for ever. (Daniel 3:58)
. . .
Spirits and souls of the just, bless the Lord; praise and exalt him above all forever. (Daniel 3:86)
The above verse show that it is ok to prayerfully address angels and the righteous dead and ask them to do something, which in the above instances include praising God, something we know that they are ready, willing and able to do.
What else might the righteous dead be ready, willing and able to do? Catholic Bibles include a credible vision that Judas Maccabeus had of the dead high priest Onias and the dead prophet Jeremiah praying for the Jewish people. (2 Maccabees 15:11-16) That the righteous dead should show such concern for the living should not come as a surprise since, according to Jesus, even the dead rich man in torment was concerned enough about his living brothers to ask Abraham to send Lazarus to warn them. (Luke 16:27-28)
The Bible includes two miracles associated with the righteous dead, namely, 1) the dead prophet Samuel’s prophecy against Saul and Israel (2 Samuel 28:19) and 2) the resurrection of a dead man when his body touched the bones of the dead prophet Elisha. (2 Kings 13:21) In Catholic Bibles, those miracles are attributed to the intercession of those dead prophets:
Even after [Samuel] had fallen asleep he prophesied
and revealed to the king his death,
and lifted up his voice out of the earth in prophecy,
to blot out the wickedness of the people. (Sirach 46:20)
Nothing was too hard for [Elisha],
and when he was dead his body prophesied.
As in his life he did wonders,
so in death his deeds were marvelous. (Sirach 48:13-14)
Now, if, as has been shown by the above Bible verses, it is ok to prayerfully address angels and the righteous dead and ask them to praise God, which we know they are ready, willing and able to do, is it not logical to assume that it is also ok to prayerfully address the righteous dead and ask them to pray for us and to work miracle for us, which, as it has been shown in the above Bible verses, they are also ready, willing and able to do?