Throwing As Usual
Under "normal" circumstances, a creature can throw an improvised thrown weapon.
Sometimes objects not crafted to be weapons nonetheless see use in combat. Because such objects are not designed for this use, any creature that uses an improvised weapon in combat is considered to be nonproficient with it and takes a –4 penalty on attack rolls made with that object. To determine the size category and appropriate damage for an improvised weapon, compare its relative size and damage potential to the weapon list to find a reasonable match. An improvised weapon scores a threat on a natural roll of 20 and deals double damage on a critical hit. An improvised thrown weapon has a range increment of 10 feet.
This will take size into account automatically, as if you're of larger size you'd compare to weapons of larger size too. So if you're throwing a rock about the size of a mace, if you're Medium it would do 1d8 damage but if you're Large it would do 2d6 damage (see Tiny and Large Weapon Damage on the same page).
Of course if you go too large you get fewer throws.
Thrown Weapons: The wielder applies his Strength modifier to damage dealt by thrown weapons (except for splash weapons). It is possible to throw a weapon that isn't designed to be thrown (that is, a melee weapon that doesn't have a numeric entry in the Range column on Table: Weapons), and a character who does so takes a –4 penalty on the attack roll. Throwing a light or one-handed weapon is a standard action, while throwing a two-handed weapon is a full-round action. Regardless of the type of weapon, such an attack scores a threat only on a natural 20 and deals double damage on a critical hit. Such a weapon has a range increment of 10 feet.
Range: Any attack at more than this distance is penalized for range. Beyond this range, the attack takes a cumulative –2 penalty for each full range increment (or fraction thereof) of distance to the target. For example, a dagger (with a range of 10 feet) thrown at a target that is 25 feet away would incur a –4 penalty. A thrown weapon has a maximum range of five range increments. A projectile weapon can shoot to 10 range increments.
This means your improvised thrown weapon can be thrown up to 50 feet (5 x the 10 foot range increment). Range isn't affected by size. Max range isn't affected by strength but accurate range is; those strength bonuses offset the range increment penalties.
Of course weapon size is different than creature size, so the intent isn't that you can throw a Medium creature if you're Medium; even a Small creature is larger than two-handed Medium weapons. If you had a pixie buddy you might make a case to the GM that he's the same size and weight as something in the weapons list so the thrown improvised rules apply.
"But but physics?" This is D&D, give it up or come up with your own creepy complex houserules like everyone did in the 1970s.
Pumping It Up
There are various rules options to allow you to throw larger items better, and especially to throw people.
The Throw Anything feat dispenses with the -4 nonproficiency penalty for throwing improvised weapons/objects. Follow it up with Improvised Weapon Mastery for a damage increase. Obviously all the other available ranged feats apply as well; if you want more range, more damage, more attacks, what have you, the *Shot feats are applicable.
The Raging Throw feat lets you use rage points to throw people into other people or things and it has damage rules specific to the feat. As a barbarian, this is probably your go-to.
The Ki Throw feat (and its various improved and other addons) let you toss an opponent. Rules for hitting and damage they take are explained therein. A monk in the pirate game I GM has this, he used it to toss a clay golem off a ship last Sunday.
The Awesome Blow feat, if you can make the STR 25 and size large requirements, gets you the ability to whack people around all the time on top of your existing attacks. It has Improved and Mythic versions too. I wrote a Brute prestige class I used in a 3.5 game based on the concept of growing to size Large and then getting this, starting from rage growth like unto Sláine's warp-spasm.