I suppose it all depends on how you define prostitution. If you look at it in its purest form it is simply a transaction in which one party agrees to provide a service to the other in exchange form some goods or service. If that's the case then pretty much anything can be compared to prostitution.
The traditional definition of prostitution is the exchange of sexual services for a good or service (usually momey). I guess one could argue that someone who sleeps with their boss for a promotion is prostituting themselves since they are providing a sexual service for a promotion.
Is a celebrity tightly hugging a fan for a picture prositution? I would argue no based on intent. Although some may say hugs can be sexual, that was not the intent of this transaction. The celebrity was making a fan happy, which is good for their own career, and making money off of it. The fan was paying for time spent with the celebrity.
Might the fan later have sexual thoughts about the encounter? It's quite possible; however, the was not the intent of the original transaction.