Plot dragging? Need to get player X into situation Z to help the rest of the group? Player turtling up in game because they don't want to get their new toys hurt (or themselves)?
Than good GM's it sounds like you need PLAYER BAIT! (tm)
Welcome to the fine art of baiting (in a good way) players into playing.
To properly player bait you need to track 2 elements in play.
The first is the character's motivation. If you are playing a classic dungeon romp game odds are there is a piece of equipment or a spell, or some class based motivation your character is seeking. Some players will just flat out tell you what they want. Others will telegraph during the game. Mind you this gets more complex in games with romance, social, or honor based plots. Sometimes the players WANT TO LOSE, but do so in a fittingly dramatic and awesome manner. Remember GM's don't be afraid to fail...with style!
The second is trickier. You need to track a player's motivation. One way to start this process is to catalog what type of player you THINK they are. (This is only for early guesses. Players are people are more complex than stereotype, but yes...I'm basically asking you to profile your players. You'll see why.) So if the player is a Builder then they tend to make things, build castles, relationships, etc. Others might be Slashers and only crave murder and bounties. Some are more chatty look to RP in character. Take quiet notes as to your guess at their top 3 motivation. This is just a guess based on your experience with them. If your guess doesn't pan out in later steps, guess again and keep experimenting with the player. You'll eventually find out what they like. Profile them as players NOT as people, duh.
Now comes the fun part. Link up the Character to Player motivations to tailor the right plot bait.
So lets give a few quick and dirty examples.
Character is Sneaky Thief and Enjoys anything dealing with getting riches or rare items for his collection; Player is introverted and worried about exposing his characters to violence, but likes doing plotting with other players. =
Player is approached by art dealer who is looking to unload a questionable artifact IF the player helps them to do this they'll get the artifact by cheating a buyer, or money by not cheating them. Either way, player has a chance to win and will risk himself a little for the prize.
It's in the comfort zone of the player. It's what they like to do and matches up with character.
Now lets get more complex:
Character is a powerful diplomat with ties to many clans. His favor seems to be to his mistress but it's doomed to failure because honor demands he marry this rival's daughter; Player is a go-get em adventure junkie 90% of the time and this time is playing a diplomat character in a very GUNG-HO manner against the traditions just for a lark. =
This player does NOT want to fail. They want to buck the odds and marry the mistress. I need to offer them a way out, a way to turn the rival to their side with out needing a marriage. Perhaps he can foil an assassination, or barter for another even bitter rival to offer peace at the price of marriage. Either way, having the character loose and die romantically isn't in the cards.
You have to play it close to the vest but over time you'll be able to read a player pretty closely. Give IN to their play styles and they'll reward you with more action and drama. Work against it if you want the game to get bumpy.
I had many players I could walk into plots and they didnt' fight. One player was known for his deals with the devil with me. I actually had him sell/pledge his soul to a higher power in a game no less than 3 times if it offered a chance to stick it to an authority figure he didn't like.
If you keep at it, you'll have openings with players to advance your games like this.
Have fun fishing!