Can I Be Sued if My Drinking Buddy Gets a DUI in Pennsylvania?
The answer wil depend on all the facts involved, such as whether the person was underage and you are considered a social host, but typically in order to find someone else liable for such acts, it needs to be shown that they hosted the event that served alcohol. In Pennsylvania, adults who serve alcohol (social hosts) to anyone under 21 may have to pay money damages if the underage person gets injured or hurts someone else because of intoxication.
To what extent you would be considered a "social host" responsible for the serving of alcohol, is a complex legal question. Two things are very important - don't serve alcohol to minors, and don't serve it to visibly intoxicated people - bloodshot eyes, staggering, slurring, or other signs. Liability is likely to attach if these mistakes are made. A primary legal question will be whether you are considered a "social host."
Under Pennsylvania common law, adults who serve alcohol at private functions are "social hosts." If a social host serves alcohol to a minor and the minor is injured or the minor injures someone else because of intoxication, the social host may be liable to pay money damages to the injured person. Social host liability only applies to adults who serve alcohol to minors. Pennsylvania law holds that adults are responsible for the consequences of their own drinking.
Here are some good links where you can get further information. Interestingly, the links provide somewhat contradictory information - the third link seems more optimistic for you in the case of adult intoxication.