You sound like you need peel/disruption and stronger dps for your team.
If you're already in game and you are falling behind, you may need to adjust your strategies or item builds. Staying where you have vision is key so you do not get caught out. Buying extra wards and placing them will help this a lot. If you want to know more about this look up warding guides.
There are a variety of items that can help you against getting steamrolled by bruisers. The two things to pay attention to are increasing your movement speed, or reducing / disrupting your opponents' movement.
Tanky items to consider include randuin's omen, Ohmwrecker, Zz'Rot Portal, and Iceborn Gauntlet.
Items for AP characters include: Luden's Echo, Lich Bane, Rylais's Crystal Scepter, Ohmwrecker, and Twin Shadows.
AD characters can build Youmuu's Ghostblade, Frozen Mallet, Phantom Dancer, Statik Shiv, Blade of the Ruined King, The Black Cleaver, Trinity Force, Zephyr, and Mercurial Scimitar.
Champions that are useful against this:
If you are playing a tank or a bruiser role try to make sure your team has several disruptive abilities, good disruptive bruisers / tanks are Zac, Maokai, Braum, Thresh, Gragas, Lee Sin, Nautilus, Sejuani, Sion, Skarner, Vi, and others I'm forgetting right now.
If you are picking a carry role, try to choose a character with mobility or cc, or both.
Mobile marksmen include: Caitlynn, Tristana (also has peel with her ultimate), Graves, Lucian, Ezreal and Vayne.
Marksmen with cc include: Ashe, Varus, Vayne, Tristana.
Mobile mages: Ahri, Ezreal, Cassiopeia (with her movement Speed bonus on q), Karma, Kennen (with lightning rush) Leblanc, Lissandra, Ziggs (with his satchel charge).
Mages with cc / dsruption: Anivia, Cassiopeia (poison cloud and ultimate), Kennen (his passive), Lissandra, Swain, Veigar, Vel'Koz, Ziggs, and Zyra.