Rambam rules that the biblical prohibition of 'hiding oneself' (lo tukhal lehitalem) means one may not avoid seeing or knowing about another's need and walk away. The obligation to help is active and personal.
הֲשָׁבַת אֲבֵדָה לְיִשְׂרָאֵל מִצְוַת עֲשֵׂה שֶׁנֶּאֱמַר (דברים כב א) "הָשֵׁב תְּשִׁיבֵם". וְהָרוֹאֶה אֲבֵדַת יִשְׂרָאֵל וְנִתְעַלֵּם מִמֶּנָּה וֶהֱנִיחָהּ עוֹבֵר בְּלֹא תַּעֲשֶׂה שֶׁנֶּאֱמַר (דברים כב א) "לֹא תִרְאֶה אֶת שׁוֹר אָחִיךָ" (דברים כב א) "וְהִתְעַלַּמְתָּ מֵהֶם". וּבִטֵּל מִצְוַת עֲשֵׂה. וְאִם הֱשִׁיבָהּ קִיֵּם מִצְוַת עֲשֵׂה: לָקַח אֶת הָאֲבֵדָה וְלֹא הֱשִׁיבָהּ בִּטֵּל מִצְוַת עֲשֵׂה וְעָבַר עַל שְׁנֵי לָאוִין עַל (דברים כב ג) "לֹא תוּכַל לְהִתְעַלֵּם" וְעַל (ויקרא יט יג) "לֹא תִגְזל". אֲפִלּוּ הָיָה בַּעַל הָאֲבֵדָה רָשָׁע וְאוֹכֵל נְבֵלָה לְתֵאָבוֹן וְכַיּוֹצֵא בּוֹ מִצְוָה לְהָשִׁיב לוֹ אֲבֵדָתוֹ. אֲבָל אוֹכֵל נְבֵלָה לְהַכְעִיס הֲרֵי הוּא אֶפִּיקוֹרוֹס וְהָאֶפִּיקוֹרוֹסִים וְעוֹבְדֵי עַכּוּ"ם וּמְחַלְּלֵי שַׁבָּת בְּפַרְהֶסְיָא אָסוּר לְהַחְזִיר לָהֶן אֲבֵדָה כְּעַכּוּ"ם:
It is a positive commandment to return an object lost by a fellow Jew, as Deuteronomy 22:1 states: "And you shall certainly return it." A person who sees an object lost by a fellow Jew and ignores it, leaving it in its place, transgresses a negative commandment, as it states Ibid.:4: "Do not see your brother's ox... and ignore it." He also negates the fulfillment of a positive commandment. If he returns the object, he fulfills the positive commandment. If a person takes a lost object and does not return it, he negates the fulfillment of a positive commandment and transgresses two negative commandments: "You may not ignore it" Ibid.:3 and Leviticus 19:13: "Do not rob." Even if the owner of the lost object is wicked and eats non-kosher meat for his own satisfaction and the like, it is a mitzvah to return an object that he lost. If, however, he eats non-kosher meat as a conscious act of rebellion against God, he is considered a non-believer. And just as it is forbidden to return a lost object belonging to a gentile, it is forbidden to return a lost object belonging to a Jew who is a non-believer, heretic, idol-worshiper or violator of the Sabbath in public.