Sounds like your pup lacks confidence. I don't think force feeding him at the dog park is a good place to do expose him to this kind of stuff, but that's up to you. Just search around and read about all the dog park horror stories. Dog parks should be for already well socialized dogs... not scared young puppies.
And if you do decide to keep going... it's really not a good idea at all to keep a leashed dog around a lot of unleashed dogs. He should either be off leash or not inside the park at all.
If you're just trying to socialize... try some group training classes instead of the chaos that goes on inside some of these dog parks. That's what I'd do at least.