Hi, we'd like someone to start receiving paid ads based on their interactions and/or stage in an engagement program. There doesn't seem to be an out of the box solution currently. How have people gotten around this? Did you build a webhook, send events with a service like Segment.io etc?
Do you mean Retargeting based on behavior within Marketo like Clicks or Opens?
I believe there are various ad tools to do this. Some require a hash (or you should do this) to keep personal information from the other systems. The tools usually use an API, although a webhook could do this too.
We have used Adroll for few of our customers to achieve this and we find it great. Like Josh said, there are few vendors on the launchpoint to help you run multi-channel campaigns.