How can I increase my speed on my hybrid bike?
It really depends on how you're lagging.  If it's because of feeling tired keeping up with them then reducing friction might be an option.  I'd suggest that the most likely reason for lagging behind is that there is a fundamental speed difference though.  See whether you're having to pedal faster than them to keep up.

Your top speed is governed by your cogs.  Take a look the number of teeth on the front and back.  If you have a 13 tooth smallest cog on the back you could get that cassette replaced with one that starts at 11 teeth.  Up front you're probably running a 46 tooth chainset whereas your road bike friends are probably running 50 teeth.  Again, you can replace that if you fancy it.  Just be careful if you do make it faster that you don't lose the low end you want for getting up hills.  You should be able to get quite a decent range with the right set of cogs.

Reduced drag from narrower tires may reduce the friction allowing you to accelerate more easily and maintain speed better but won't affect your top speed appreciably.

Clipless pedals may allow you to improve your efficiency with pedalling.  I would only look at these when I was happy with a bike though, rather than as a solution to a problem like that.

Update:  Based on zenbike's comment I'd say the switching to a road bike warrants more consideration.  Assuming it is the gears he's right that a hybrid may well be difficult to alter to run the gear ratio you want to keep up with your friends.  When thinking of getting a new bike take a look at how similar it is to the ones your friends ride.  Simply getting a cheap heavy one if they have light racers may well leave you with a similar problem.  

If 2 bikes have the same gear ratio but one is heavier it will be able to go as fast, but it'll be more effort to get it up to speed, and a little more effort to cruise at the same speed.  It's less of a problem than not having the right ratio, but you'll probably find your self lagging a little at first.