1. The question should divided to two: Halachic and moral.
2. Halachic discussion is twofold as well: A. Hilchos Tzedakah, B. Hilchos: i. Lifnei iver ii. MeSaye’ah. [This is assuming that the issur of smoking is unequivocal. This can be debated, though not in this venue. (A doctor told someone I know that one cigarette a day will not harm him.)]
Disclaimer: Although I am far from having reached the level of asukei shma’atsa aliba de’hilchisa, I would like to suggest some points, leaving the verdict for those more qualified.
A. Hilchos Tzedakah: The halacha requires us to provide the destitute with their needs, ‘Dei Machsoro’ (this is not translated as luxuries). This probably does not include feeding an addiction (aside, perhaps, for one of coffee 😉 )
However, giving funds (cash, check, wire, transfer, or money order) as opposed to providing the cigarettes directly, is not necessarily considered providing for the addiction, provided that he has other things to spend money on (such as shoes for his children for yom tov). More on this contrast below.
B. i. Hilchos Lifnei iver, ii. MeSaye’ah: This involves two very complex, and though often intertwined, distinct sugyos. It would seem:
i. Because the pauper presumably has enough money on him to purchase cigarettes, this would probably be considered ‘Chad ibra de’nahara’ (same side of the river), and would not constitute Lifnei Iver.
ii. Since he is not providing cigarettes, but money, this probably does not constitute MeSaye’ah.
Since halachicly there is no compelling reason not to give, you would still be left with your mitzvas aseh of tzedakah, and issurim for turning the ani away.
3. Moral question is basically do I refrain from giving a child who is in dire need for money because he is likely to use some of his money to buy a knife, which he may use to hurt himself.
Since your intention is altruistic, to provide the ani with his (unalienable) necessities, you can assume that your money will be funneled toward that specific cause. This as per the famous story with Reb Chaim of Volozhin.