I won't ask you why you missed the meeting, my advice would be the same. Call your PO. If you can reach him/her say you missed and want to come in as soon as possible. And then follow through by showing up. If you can't reach the PO directly, leave a message even if it means going to their office and leaving a note with the receptionist. The idea is to be straight up and show that you are willing to make up the visit.
If a warrant has issued, find out which court the case would be heard in and when they deal with probation matters. At this point it might be helpful to have an attorney to call the prosecutor and the PO to see if the warrant could either be quashed or arrangements made to show up at court to have the judge hear the matter without you having to sit in jail waiting for a date.
You did not say if this was a misdemeanor case, a felony, or whether it is DOC community custody. If it is a violation of community custody the matter is heard before a DOC hearing officer. In these DOC hearings not only are you not entitled to an attorney, if you have an attorney he/she is not allowed to participate. (I know this sounds wrong but it would take too long to explain here).
A word of caution: you are very likely to be drug tested after missing a meeting, so keep it clean. Good luck.
As previously stated. You need to call your probation officer and tell them you would like to reschedule. Its been my experience that if you're in compliance with your probation (i.e., treatment, appointments, staying out of trouble) then you should be fine.