Is one who guides his friends to a liquor seller, after having advised them, sinful, and does the Hadith "The one who guides to something is like the one who does it" apply to him?

You fell short in denouncing these individuals. You should have moved to other levels of denunciation after advising them, such as reproaching and harshly scolding them with stern words. Scholars have mentioned that there are five levels of Hisbah (enjoining good and forbidding evil): defining (the good and evil), admonition, reviling and harsh reprimand, forceful prevention, and intimidation and threatening with physical punishment. If you directed them to someone who has no connection to what they want, merely to get rid of them, there is no sin upon you if that person was their means to their forbidden aim. However, your action is considered a weakness and a shortcoming in deterring them. Therefore, you must seek forgiveness, repent, and continue to advise them.